Dr. H. P. Olmo

University of California, Davis 1952


My purpose in presenting this talk is to survey the principal lines along which varietal improvement work of winegrapes has been progressing at Davis for the past 20 years, so that you may have some idea of "wine grapes of the future", some of which are now undergoing trial here and at Oakville.  During the harvest season some of you will be able to see these varieties, in trial blocks.

The principal factors entering into the quality of a wine grape that are largely inherent in the variety itself are the acids, sugars, tannins, coloring matters, and the aromatic and flavoring substances.  Since the presence and amount of any one or more of these substances influences the discernment of the others, it is impossible to give a definition of just what a fine quality variety is, except to say that when grown in a proper environment and manipulated by a competent winemaker, a fine quality wine can be produced.  But this is only begging the question.  Fortunately widespread experience has shown that certain varieties are more desirable than others for wine, but unfortunately we must often lean heavily on the longer European experience obtained under quite different conditions of soil and climate, than our own.

There is every reason to suspect that the wine grapes of tht- future will combine heavy and more constant yield with high quality of the product.  This is the surest and most direct way of improving the quality of our wines in short, make it economically profitable t-- do so.

First let us consider some of the important quality factors of the grape.

Acidity:        The composition of grapes at harvest time from celebrated European table wine districts as compared with those of California, differ most markedly in the higher total acidities and the lower pH at the same sugar content.  It is evident that the varieties now recommended for fine wines in California, especially Pinot blanc, Chardonnay, Pinot noir, and White Riesling; are often too deficient in acid to produce the best quality obtainable under even the cooler climatic zones where grapes are grown in California.  It is, therefore, necessary to correct this deficiency by blending with high acid varieties of poorer quality, picking too early before a sufficient sugar-acid balance has been reached, or adding acid to the musts before or after fermentation.  Quality varieties are needed that will more, consistently produce a well balanced must under our favorable growing conditions.

This was early recognized as an important problem that might be solved by breeding new forms.  In 1935 seedlings of Tannat were grown in order to isolate breeding stock that might transmit high acidity to their progeny.  Tannat is characterized by a high sugar content as well, besides being a good producer and a vigorous variety.  Of 42 seedlings brought to fruiting, several had a combination of very high sugar and high total acid.  One of the best selections had an average acidity of 1. 26 at 260 Balling, in otheer words, both sugar and acidity far surpassed the parent variety.  In 1941 this selection Was crossed with Semillon and also White Riesling.  The purpose of these crosses was to introduce the desirable flavors and other quality factors missing in the Tannat seedlings.  Nineteen new varieties are now on trial, and all but the best one will be eliminated.  This program has also furnished selections with a wide range of total acidity, that are to be tested for brandy production this year by Dr. Guymon, in an attempt of determine whether high or low acid selections are best for brandy.

Although both tartaric and malic acids are present in appreciable amounts in the total acid complex of the vinifera grapes so far studied, this does not appear to be the case in many of our native species that have been so widely used by French hybridizers.  Undoubtedly a study of these varieties will uncover different relationships.  It appears likely that future wine grape varieties might be bred to either increase or decrease a given constituent of the complex, as well as the relative amounts combined or free.  Many of the labrusca hybrids, such as Concord and Catawba, do not have the same acid balance as vinifera.

In some wine grape hybrids derived from vinifera x riparia and vinifera x berlandieri crosses, fruited at Davis, the acidity may be built up to a range much beyond that of our cultivated viniferas, over 3 grams of total acid as tartaric per 100 cc of juice.  These selections have not been propagated for wine tests but it shall be interesting to do so.  In general therefore, high total acidity may be obtained from several native species as well as from vinifera, but it appears necessary to delve further into the acid complex of the hybrids.

Aromatic and flavoring substances: These often determine those subtle differences that distinguish high quality wines.  They are most often present in the ripe fruit itself, but may develop during the wine-making process or aging.  The term bouquet is often used as signifying those developed in the wine, in contrast to the flavoring constituents or aromas detected by smell or taste of the fresh grapes.  This distinction is not often justified, since apparently each grape furnishes a substrate of materials capable of bringing about the transformations that occur.  It is probable that other constituents of a variety may have a conditioning effect on the quality of these aromatic substances.  One cannot obtain a Cabernet aroma from a Zinfandel, regardless of the method of fermentation or aging.  Thus in the production of the important aromatic materials we must still rely on the source in the grape variety, until chemists are able to understand these substances and synthesize them cheaply.  

The chemical nature and formation of the aromatic substances is the most neglected in the whole field of enology, considering their great importance in the mature wine.  This lack of knowledge delays the breeder in understanding the inheritance of aromatic substances.  We have noticed repeatedly that the muscat aroma tastes differently when transferred to other varieties.  Is this a question of quantity of a single material, or is it inter-reaction with other substances on the taste, or are several compounds involved?  Until adequate chemical tests and isolations of these substances can be obtained, the breeder must do his job by trial and error method.

Actually the cultivated vinifera grape has a wide assortment of aromatic sub stance s, but many do not, appear to be in high concentration.  We have made small wine samples of several native species.  The aromas of practically all are much higher and more potent whan our well known aromatic types of vinifera.

The strong "foxy" aromas varieties like the Concord, Catawba and Niagrara are well known.  This aromatic material is derived from the Vitis labrusca, the most common native grape along the Atlantic seaboard, particularly New England.  Yet there are many different kinds of aromas that are called "foxy".  Almost each hybrid variety has a distinct flavor of its own.  The Isabella is often called "the strawberry grape" in Italy.  The Delaware has been compared to some vinifera grapes in its more delicate aroma.  The Agawam when used in hybrids with vinifera at Davis has given a series of wholly unusual and distinct flavors that are unlike those derived from Concord or Campbell.

It might surprise you to know that a single mature berry of the ratundifolia or "Muscadine" grape, left on the office desk in the evening, can be easily detected by its odor on entering the office the next morning.  The aromas of the Muscadine wines are so intense that they are unpleasant.  Yet when diluted down, such an aroma is pleasing to many people.  At least one commercial wine company has made a very popular wine brand, which depends on this wild species of the southern United States to add its distinct flavor to the vinifera blend.

To the selective palate experienced with European type wines, the aromatic constituents of many labrusca-type and other native wines-are too pronounced and dominating.  Yet there are large segments of the population in this country who have acquired a liking for them, as witness the commercial success of "Concord-type" wines.  There is almost a virgin field for the production of new varieties with new. flavor and aroma blends.  Two years ago we started a wine survey of many native species and hybrid varieties with the objective of discovering new and desirable aromas and flavors.  The tasting results are uncovering some surprising reactions.

When the Cabernet flavor is transferred by breeding to a white variety, it is no longer recognized even by experienced tasters as being Cabernet, yet these wines may be fragrant and extremely pleasant.  What has happened to it? Are the pigments and tannins a factor in the discernment of this flavor, or is it more than a single entity and capable of partition?

Coloring matter and tannins: The traditional color of red wines is deep ruby red with a slight tinge of purple, and of white wines, amber to golden.  No one knows whether the American public would prefer colors of different hues.  The purple color of the Concord has been widely accepted.  The French have considered many red wine hybrids to produce very poor quality wine, but it is interesting to note that in their tasting remarks color is rarely at fault.  Yet many such hybrids are more purplish than vinifera varieties.  There is a widely held view in commercial circles that it is necessary to have a red wine heavily colored, and considerable attention has been given to methods of extracting more color in the preparation of both red table and dessert wines.  Yet to some people wine observed in a glass is more striking and beautiful if the color is not as dark as many of our standard burgundies.  Few Americans hold the glass of wine up to the light for examination, in fact they often dine in areas with subdued lighting, when darker colors cannot easily be noticed, Blending with high color varieties is often resorted to, but varieties like those recommended, such as Salvador, are only adding poor quality wine to good.

The necessity of having a stable color that does not change to a brownish caste and does not leave a heavy precipitate in the bottle is generally agreed upon.  It is not particularly difficult to breed varieties having high color with good stability.  At the present time we have many selections of new port wine varieties in this category, in which the color is sufficiently intense and stable.  In table wines, the new Ruby Cabernet combines an attractive and stable color more intense than the Cabernet Sauvignon.  Hybrids of the Zinfandel now being selected at the Oakville station have corrected the poor color content of this variety, yet they retain the typical flavor of the Zinfandel parent.

In the production of new white table wine varieties our efforts have been to produce wines of greenish caste that would be less subject to oxidation and browning than those now available.  This work could be hastened, if the chemical background of oxidation in white wines was better understood.  Selection of promising varieties is done in an arbitrary but effective fashion by fermenting half-gallon samples of must, and allowing excess aeration of the wine before bottling.  Those showing or tasting of marked oxidation after a year' s time are eliminated.  Among the several thousand seedlings tested for dry wine since 1942, we have uncovered a range of colors not found in commercial types.  Some practically are devoid of purple pigments, others are orange-red, others various shades of pink and purple.  White wines are likewise variable, but the differences are less conspicuous, vary from green to water white, most are golden.  The question of what is the best color cannot be settled arbitrarily.  It is indeed possible that the American sense of color values is quite different than the European.  Once the public has a chance to express its opinion it is possible that our new varieties of the future will. take such preferences into account.

Yield.  Many noted viticulturists and enologists have long been dogmatic in their belief that "high quality in wine is always associated with low-yielding varieties".  There is at present certain support for this statement, since the Pinot noir of Champagne and Burgundy, the Cabernet Sauvignon of the Gironde, the Chardonnay of Chablis, the White Riesling of the Rhine and Moselle are all notorious for their skimpy crops.  If this doctrine were to be accepted, we have before us a rather dismal chance of producing new varieties of quality that would also produce a respectable tonnage for the grower.  Fortunately there are already exceptions to the rule.  The Semillon, which is the base of Sauternes, is year in and year out, at least better than an average producer.  The Chenin blanc or "White Pinot" which I first identified in California in 1939, has produced in some areas a quality wine, yet it is certainly a heavy-yielding variety.

Varieties that consistently bear large crops often fail to produce mature fruit of balanced composition.  The Carignane is an excellent variety for the grower, but the fruit often fails to reach good maturity and is not as well accepted by the winemaker.  For some varieties, such as the Burger, our heaviest yielding white-wine variety, even with short pruning, a balanced maturity is seldom possible unless severe cluster thinning is resorted to.  However, heavy yield does not necessarily indicate a failure of the fruit to reach a balanced maturity.  The Black Malvoisie is capable of very heavy yield, especially for the small size of the vine, and it is rare that such heavy crops do not reach a high balling degree.  Thus, there are very wide inherent differences between varieties in the efficiency with which they perform, as to the amount of fruit that can be brought to maturity.  In our breeding work at Davis particular attention has been given to these inherent differences.

Uniformity in yield is desirable.  Many varieties will tend to over-crop in certain years, even though the customary pruning practice is not changed.  This often weakens the vine and of course eventually produces fruit of poor quality.  Some Zinfandel x Carignane hybrids have been tested that in the first few years of trial were producing wine of very good quality and the crops were very satisfying, averaging almost 10 tons to the acre at St. Helena.  All of these have had to be discarded, because after five or six years of bearing the vines were exhausted.  The control of crop would have been necessary by heavy annual thinning, but this extra labor is not-warranted.  Some varieties have a self-regulating mechanism of not overcropping.  This is particularly true of the Cabernet Sauvignon and the new Ruby Cabernet.  Despite the fact that a large riumber of canes be left at pruning time (light pruning), the total crop cannot be increased as much as one would expect.  The reason for this is that a heavier drop of blossoms occur just after set, and the clusters and berries remain smaller and looser.  Thus the vine usually always retains good vigor and matures its charge of fruit regularly.

Disease and insect resistance: Resistance to diseases and insects is important because these factors influence the yield and quality.  The vinifera grape is of Middle-Asian origin and it is susceptible to many American ' diseases and insects that were apparently never present in its homeland.  In California, the most troublesome disease of the foliage is powdery mildew, Uncinula necator.  This disease is readily prevented by dusting with sulfur one or more times during the growing season.  As many as six treatments have been recommended.  But it is well to take account of the fact that this treatment uses approximately 15,000 tons of dusting sulfur annually and costs over two million dollars to apply.  In years of severe damage, crop loss is considerable.  There are very marked differences in resistance between varieties that are inherited, so that the breeder could bring in resistance without much effort.  Progenies of all common varieties have been tested by inoculation in the greenhouse.  Certainly our varieties of the future will be resistant.  Selection for resistance has been discontinued because greenhouse space is now allotted to other projects.

The root aphid or phylloxera has forced the use of rootstocks in infected soil areas, which include most of the wine grape regions of the North Coastal areas and the heavier soil types of the San Joaquin and Sacramento Valleys.  Although this problem has been satisfactorily solved by the use of resistant rootstock varieties such as V. rupestris St. George, other problems have come in the wake of re-establishing vineyards that were one on their own roots.  A grafted vineyard is much more expensive to establish, it is shorter-lived, and the incidence of transmissable diseases of virus nature increases tremendously.  The ideal solution is to obtain fruiting vines with resistant root systems, a quest that was once started in France with considerable gusto during the 1880's.  However, amateur but devoted breeders were so entranced by the other disease-resistant qualities of th e hybrids that this original quest was soon lost sight of, and the new hybrids are now known simply as hybrids and not "direct producers".  Even though selection for phylloxera resistance no longer was uppermost in mind, it is all the more remarkable that some can be grown on their own roots in favorable soils and live long enough to be commercially profitable.  The source of this resistance has been derived chiefly from V. rupestris, but V. riparia and V. lincecumii also were used in some hybrids.  No genetical evidence is available. to indicate that resistance to this louse and high quality of fruit cannot be eventually combined in the same plant.  This objective can certainly be accomplished when and if a large breeding program can be supported.

In the sandier soils of the valley floor, root-knot nematode is often troublesome, and more recently the  root-lesion nematode is also suspected of damaging vine root systems, even those of our common phylloxera-resistant stocks.

V.      champini, a native grape of Texas, has been used as a source of root knot nematode resistance and rupestris and riparia as a source of phylloxera resistance.  In the Spring of 1942, 700 hybrid seedlings were grown in the greenhouse in galvanized tanks in soil heavily infected with phylloxera.  This technique was so successful in building up phylloxera that many seedlings were killed during the first growing season.  The surviving seedlings were then tested for another three years in outdoor beds in heavily infected soil.  A few more became weak and were eliminated.  During the period of the phylloxera test a parallel lot of seedlings from the same crosses were tested for root-knot resistance, in the same manner as for phylloxera, most we found to be resistant, so there was reason to believe that plants resistant to both insects could be easily obtained.  The most promising plants were set in the field for propagation tests (the cuttings of a resistant stock must root and graft well).  

These plants are being tested further for resistance to various strains of nematode by Dr. Lider, and for resistance to drought by withholding all irrigation.  Commercial trial of several of the best plants will now begin by grafting fruiting varieties upon them and continuing observation of them for some years.  The production of a rootstock resistant to both phylloxera and various strains of root-knot nematode has thus been accomplished.

Since the cause and effects of Pierce's disease have become widely known, more attention has been focused on the ravages caused by transmissable viruses.  The list of such diseases is growing yearly.  For some of them, like Pierce's disease, no solution to the problem has been suggested except to breed resistant varieties.  Since resistance is rare and not present at all in the best cultivated grapes-. it will require time and effort to transfer the resistance of native species into desirable fruiting varieties.  After testing over 400 varieties and species in badly infected areas at the University of California at Los Angeles, resistance has been discovered in several varieties of vinifera and in V. trealeasei, a native grape of New Mexico.  The next step is to incorporate these sources of resistance into more desirable cultivated varieties.

In the testing of new wine varieties it is difficult to obtain an objective opinion that is truly scientific.  The most formidable obstacle in the selection of a new wine variety is to evaluate the wine samples, which relies upon an organoleptic examination.  As all of you realize, taste and smell cornprehension are inherited in an exceedingly variable manner and are conditioned by past experience and memory as well as the mental and physical condition of the individual.  Obviously a. sampling by one or a few tasters is subject to large error.  In vineyard trials, new varieties are often looked upon w ith suspicion, or if they are tried, many growers expect a miraculous performance.  One of the chief bars to progress is the feeling of many growers that an improved variety jeopardizes their established variety plantings, and do not even try a fair comparison with what they have.  In the future one can expect that the varieties supplying the raw material will change more rapidly than before, for two reasons.  The first is that improved varieties will be available, and secondly, growers will become educated to try new varieties more quickly to maintain their advantage in competition.  There is one advantage in the adoption of new wine grape varieties that has tremendous significance for the future of the wine grape industry.  We could truthfully say that the grapes and wines are first and foremost typically Californian.  Gradually we will be able to loosen our grasp of those apron strings that fan out from Germany, France and other mother countries of Europe.  Until then we are cast in the role of imitators and we must and should continually acknowledge our indebtedness.


 Harold Olmo received his BS degree in Horticulture in 1931 from UC Berkeley, followed by a PhD in Genetics from UC Berkeley in 1934.   He then worked as an Associate in the Experimental Station before beginning his career at UC Davis as an Assistant Professor of Viticulture in 1938.   Dr. Olmo retired in 1977 with a legion of awards and merits, which continued to be bestowed upon him during his emeritus years.

 This San Francisco native received The Wilder Medal of American Pomology Society in 1958, The Laureate and Medal for Outstanding Contributions to World Viticulture, by the Office International de la Vigne et du Vin, Lesbon in 1965, The Charter and Honorary Life Member, American Society for Enology and Viticulture in 1973, The Award of Merit by the American Pomology Society in 1974, The Papal Medal, Benemerenti by the Catholic Church in 1979, and the Rockefeller Spirit of Service Award, International, Executive Service Corps in 1993.   He was a Guggenheim Fellow, Fulbright Scholar, and a consultant to the United Nations for over twenty years.  


Dr. Olmo traveled the world extensively acquiring and searching for grape varieties and species for use in his breeding program, which he amassed into one of the world's greatest grape collections.   His exciting travels through Afghanistan and Iran led him to be nicknamed the "Indiana Jones of Viticulture".   Wherever you travel his name is recognized for his academic and practical contributions to regional and world viticulture.   Dr. Olmo released 29 grape varieties over his university career including the widely grown Redglobe, Perlette, Ruby Seedless, Ruby Cabernet and Rubired.   He donated hundreds of thousands of dollars in patent royalties from his varieties back to the Department of Viticulture and Enology where the endowment is used to assist new faculty and graduate students.


While developing and commercializing new grape varieties, Dr. Olmo contributed knowledge to nearly every aspect of viticulture, including the development of new trellising and mechanical harvesting methods.   He long considered his most important contribution to be the formulation of the first grapevine certification program to insure clean and selected plant material.   However, it is likely that the contribution he will best be remembered for was his mentoring of countless students, colleagues and viticulturists across the world.


The public is invited to the rosary, which will be held at Davis Funeral Chapel, 116 D Street, Davis, California on Thursday, July 6th, at 7:00 p. m.   The funeral services, also open to the public, will be held at St. James Catholic Church, 1275 B Street, Davis, California on Friday, July 7th, at 1:00 p. m.   A celebration of his life will immediately follow in the St. James Fellowship Hall.   Plans are underway for a memorial service on Sunday, July 30th, the eve of his 97th birthday.


A tribute from FPMS Grape Program Newsletter Page 12


Harold P. Olmo, 96; Had Key Role in Growth of California Wine Industry
By Mary Rourke, Times Staff Writer
July 8, 2006

Harold P. Olmo, a grape breeder and viticulturist who played a key role in the development of the California wine industry starting in the 1930s, died June 30. He was 96.

For years Olmo was known as the Indiana Jones of viticulture for his travel adventures on horseback and camel in Central Asia during the 1930s and '40s to collect endangered vines that he then cultivated in California.

He had been hospitalized at the Sierra Health Care Convalescent Hospital in Davis, where he died of complications from a fall, said Lynn Alley, who is writing his biography.

Olmo had been on the UC Davis faculty in the department of viticulture and enology since 1938, including 29 years as professor emeritus.

His "breadth of knowledge and his adventurous spirit were critical to the reemergence of viticulture in California," Andrew Waterhouse, interim chairman of the department, said in a statement this week. The grape-growing industry took several major dips during Olmo's time, most recently in the 1950s.

Along with propagating rare species of grapevines that he gathered in Pakistan, Afghanistan and Iran, Olmo bred close to 30 new varieties, including the ruby cabernet, a wine grape. Most of his new varieties, however, were table grapes, including the popular redglove and perlette, the first grape he introduced commercially, in 1948. He also bred raisin grapes.

Over 70 years he amassed one of the world's most important grape collections, Andrew Walker, Olmo's successor as grape breeder and geneticist at UC Davis, said in an interview this week. The collection is housed on university property and serves as a library for students and faculty, as well as for growers.

Cuttings from some of the wild vines that Olmo collected in Afghanistan decades ago were recently sent back and planted there after the vines had become extinct in that region.

California vintners know Olmo as the man who made the chardonnay the most widely planted wine grape in the state. Through the 1950s the chardonnay produced a comparatively low yield. Olmo developed a variety with larger clusters and greater disease resistance.

Its success led to a steady rise in acreage planted with chardonnay vines. The number went from 50 acres in 1960 to 100,000 acres this year, Walker said, adding that the total number of California acres planted with grapevines is 900,000.

Vintners around the world consulted with Olmo about the suitability of grape varieties to their climates and terrains. Olmo's Reward, a Bordeaux blend made in Australia, is named in his honor.

Born July 31, 1909, in San Francisco, Olmo graduated from UC Berkeley with a degree in horticulture and went on to earn a doctorate in genetics at the university. During his academic career he was awarded both a Guggenheim and a Fulbright fellowship.

He married Helen Miller, and they had three children: daughter Jeanne-Marie Olmo of Davis, and sons Daniel Martin Olmo of Davis and Paul Stephen Olmo of Port Orford, Ore.

Olmo's wife died in 2000. He is survived by his children, grandchildren and great-grandchildren.