UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA POLLINATION OF THE SWEET CHERRY BY WARREN P. TUFTS AND GUY L. PHILP BULLETIN No. 385 March, 1925 UNIVERSITY OF CALIFORNIA PRINTING OFFICE BERKELEY, CALIFORNIA 1925 POLLINATION OF THE SWEET CHERRY By WARREN P. TUFTS and GUY L. PHILP In 1913 Gardner 1 published the results of rather extensive polli- nation studies with sweet cherries and showed that all varieties tested are self -sterile under Oregon conditions. Hedrick, 2 in 1915, stated that sweet cherries as grown in New York appear to be, for all practical purposes, self-fertile. More recently Wellington 3 working in the same state, made the following statement : 1 ' Sweet cherries are practically self -sterile, and in fact many varieties are inter-sterile." Crane 4 reports that all sweet cherries which have been tested in England are found to be self -sterile, and that in a number of instances there appears to be incompatibility between varieties. He also calls attention to the fact that there appear to be "strains" existing within certain of the cherry varieties. Hooper, 5 another English investigator, finds conditions similar to those reported by Crane. Florin 6 reports that in Sweden numerous Bigarreaus and Hearts are practically self-sterile and therefore require cross-pollination to set fruit. These facts, together with reports of crop failure in many cherry orchards in different sections of California, indicated the need of accurate information on this subject and led the writers to conduct rather extensive experiments during the years 1916, 1917, 1918, 1919, 1920, 1922, 1923, and 1924. The work has yielded some interesting results, which are presented in this paper. The data secured do not permit the drawing of final conclusions, so that it is essentially a progress report. PROBLEMS OF SWEET CHERRY POLLINATION In planning the work, the writers had in mind the differences of altitude, climate, and soil, that exist in various parts of California and have attempted to answer the following questions for these various conditions ; 1. Will sweet cherry varieties, when planted in solid blocks, i.e., without pollinizers, be commercially profitable? If so, the varieties may be classed as self -fertile ; if unprofitable, then they should be classed as self -sterile.* *The writers prefer the terms lt barren' ' and - 'fruitful' ' as explained by Kraus in the Journal of Heredity, Vol. 6, No. 12, pp. 549-557, 1915, rather than the inexact terms "sterile" and "fertile." The latter terms have been used in this paper because the general public is more familiar with these expressions. 4 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 2. If cherry varieties are self -sterile, what varieties may be planted together to produce profitable crops? This is a question of inter- fertility. S-X^NXvGX^t '"Coo TcLV ^oo^e S^C&cu, o \w cx'b cuAtcxA^cL Fig. 1. — Showing the different stages of bloom from a pollination standpoint. (1) Immature; (2) Too far advanced (several petals removed to show flower structure); (3) Proper stage for emasculation; (4) Emasculated. Bulletin 385] pollination of the sweet cherry 5 3. When planting inter-fertile varieties together the following points should always be considered in selecting the pollinizers: (a) Coincidence of bloom of pollinizer with that of the variety to be pollinated. Fig. 2. — Typical branch for emasculation. Note the large percentage of blossoms at the proper stage of maturity for emasculation. 6 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION (b) Germinability of pollen produced by the pollinizer. (c) Amount of pollen produced by pollinizer. (d) Commercial value of pollinizer. (e) Succession of ripening for convenience of harvesting. ORGANIZATION OF THE WOEK The methods employed were those commonly used in cross-polli- nation experiments. The work consisted in first removing the stamens and then applying the pollen desired (figs. 1 and 2). Exact counts of the artificially pollinated flowers were made and the fruits resulting from them counted at harvest. Experiments were conducted at Davis and Vacaville in 1916-1920, at Watsonville in 1916, at San Leandro in 1917, at Santa Clara in 1920, in the Occidental district of Sonoma County in 1922 and 1923, and in Placer County in 1924. In these experiments about 67,000 blossoms were self-pollinated, 300,000 cross-pollinated, and 290,000 counted to determine the normal set. THE BLOOMING PEEIOD OF CERTAIN CHERRY VARIETIES Cherries have a comparatively long blooming period if the whole time from the opening of the first flowers to the shedding of the last blossoms is considered. The average length of the blooming period for most varieties is about two weeks. This period may be nearly a month in certain seasons. Weather conditions during and just pre- ceding the blooming period have a marked influence upon the length of the period of bloom and also upon the dates of blooming. Because of climatic conditions, the dates may vary as much as three or four weeks in different seasons. Varieties, however, keep approximately the same order of blooming each season. From observations in the Vaca Valley for four years, the following varieties may be divided into early and late bloomers. They are listed in their order of earliness. Early Bloomers Late Bloomers Advance Rockport Chapman Pontiac Black Heart Bjng Early Purple Napoleon Black Tartarian Lambert Burbank Black Republican Bulletin 385] POLLINATION OF THE SWEET CHERRY Under most conditions, Black Tartarian and Black Republican overlap the varieties in the second column enough for cross-polli- nizing. The accompanying chart, figure 3, gives the average period of effective bloom for certain cherry varieties as grown in the Vaca Valley for the years 1917 to 1920, inclusive. The term effective bloom is used to designate the length of time the tree is in conspicuous blossom. Periopot Effective Blcwi or Certain Cherry Varieties Vaca VALLLy-CAuroR/iiA 1917 to \320~lncL\JSNt ycARS Black Heart 4 Black Tartarian a Ghapma/s 4 Apva/mch 3 Early Pi/rple a BvRBA,NK 4 Black Republics a Pontiac A Bl/1G 4 /Iapoleon 4 rockport 3 Lambert a MARCH APRIL £ CJ n l3 3/ .' ■/ ft fl /ft 11 iv Fig. 3. — The period of effective bloom of certain cherry varieties, covering a period in nearly all cases of four years. The number of years averaged is shown in a separate column for each variety. ABUNDANCE AND VIABILITY OF POLLEN In order to secure the best results under field conditions from cross- pollination, it is necessary to have varieties which are good pollen producers. Fortunately, most cherry varieties are satisfactory in this respect as indicated in table 1. TABLE 1 Kelative Abundance of Pollen Produced by Different Varieties Variety Pollen Production Variety- Pollen Production Abundance Medium Giant Abundant Advance Medium Knight Abundant Black Heart Medium to shy Lambert Medium to abundant Black Bepublican Medium Major Francis Abundant Black Tartarian Medium to abundant Schmidt Abundant Bing Medium Waterloo Heart Abundant Burbank Medium Windsor Abundant Centennial Shy Wood Abundant Downer Abundant Early Purple Medium to abundant 8 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION To determine whether the pollen to be used was viable, each sample collected was tested in a 12 per cent cane sugar solution. While cherry pollen is not as viable as the pollen of some other fruits, in most cases a satisfactory artificial germination was secured. Where possible a new collection of pollen was made when satisfactory results were not obtained with the pollen first collected. There seems to be a close correlation betwen the abundance and germinability of the pollen and the weather conditions just preceding and during the blooming period. Warm, clear weather is favorable to an abundance of pollen of high germinability, while cold, cloudy weather results in a scant amount of pollen of low germinability. There is a wide range in the percentage of germination among different varieties and also in the same variety at different places in the same and in different seasons. As much as 3 to 88 per cent variation in the pollen of a single variety was found in differnt localities during one season. The writers secured on the average an artificial germination of about 30 per cent. This was considered satisfactory. In certain crosses, a 30 to 50 per cent set resulted from using pollen with only a 3 to 5 per cent artificial germination. The preceding figures seem to indicate that a low artificial germi- nation does not necessarily mean that a poor set will result. However, since so many factors determine the setting of fruit, it seemed advis- able to avoid the use of pollen of low viability, which might tend towards further confusion in interpretating the results. NORMAL SET OF CHERRY VARIETIES Immediately after the petals fall, each flower begins to form a fruit. During the following two or three weeks a certain percentage of these young fruits, for reasons not fully understood, drop off, leaving only a rather low percentage of the total number of original blossoms to continue development. It is quite necessary that this drop take place, as the tree under average circumstances would not be able to carry so many fruits through to maturity. The exact factors determining which of these young fruits shall drop are not known at present. Later in the season still another falling off of the young fruits occurs. This is known as the ''June drop." The expression ''normal set" is used to designate the percentage of fruit which sets under normal conditions when the tree is left open to insect pollination. The normal set may be determined at any time up to the end of the season by counting the fruits on a tree and com- Bulletin 385] pollination of the sweet cherry 9 paring this number with that of the blossoms. In these experiments, approximately, two thousand blossoms of each variety, well distributed over the trees, were counted each year and records made of the normal set after the first drop, after the second drop, and at harvest time. The normal set is used for comparison of the different crosses. A study of the normal set in table 3 indicates that most varieties set a good crop in 1916, 1917, and 1920. A few varieties failed to give a good crop in these years. Indi- vidual variations and condition or vigor of the trees may be partly responsible for the shortage, though all the trees used appeared to be moderately vigorous and received good commercial care. The normal set on these same trees during the years 1918 and 1919 was far below the average, mainly because of drought and a heavy frost during the blooming period in 1918. It was also noted that there were few bees in the orchard during the blooming period of these years. SELF-POLLINATION OF SWEET CHEEEIES During the years 1916 to 1924, inclusive, the following varieties of sweet cherries were tested for self -sterility : Abundance, Advance, Black Bigarreau, Black Heart, Black Republican, Black Tartarian, Bing, Burbank, Burr Seedling, Chapman, Centennial, Cleveland, Downer, Early Purple, Lambert, Major Francis, Mezel, Pontiac, Rockport, Schmidt, Napoleon (Royal Ann) (fig. 4), Waterloo Heart, Windsor, and Wood. In addition to these a number of promising seedlings and strains were tested. They were tested for from one to six years and in no year or locality did any variety give a satisfactory set of fruit when self -pollinated, as is shown by table 2. The Bing, during the season of 1917, set a 3.5 per cent crop with its own pollen, but the same year the normal set was over 20 per cent. From a com- mercial standpoint, all sweet cherries thus far tested under California conditions may be considered as self -sterile. It is therefore inadvisable to plant any of the commercial varieties alone or in solid blocks. POLLINATION REQUIREMENTS OF CERTAIN CHERRY VARIETIES The facts presented in table 3 are based on the results obtained from pollination experiments conducted in the Vaca Valley during the years 1916 to 1920, inclusive. The data secured in other experiments conducted at Watsonville, San Leandro, Santa Clara, Occidental, and Newcastle have been omitted because they would not in any way alter the conclusions. 10 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION The results of certain crosses are difficult to analyze and in some instances have been discarded in the discussion. This is particularly true for the year 1918, when a severe frost was largely responsible for the poor sets obtained. Fig. 4. — Napoleon X Self. No fruit set on a branch of Napoleon which was pollinated with its own pollen. A typical case of Napoleon when self-pollinated. Bulletin 385] POLLINATION OF THE SWEET CHERRY 11 TABLE 2 Self-Pollination. Summary for All Locations 1916 1917 1918 1919 1920 1922 1924 Varieties co a o co co — CO IO 20 30 40 SO O !0 20 30 '70 $> O /O 10 30 43 JO O /O £0 30 -M 50 O /£> & 5Q 40 SO /Formal Set x5elf xBlack Republican xBl ACK TaRTARIA/H xCaplv Purple xLambert x/Sapoleovm xPo/ITIAG . _ ■ 1 L_ 1 ^_ Fig. 5. — This chart shows the influence during the seasons of 1916 to 1920, inclusive, of various kinds of pollen when applied to the flowers of the Bing variety. Note the failure to set fruit when self -pollinated; also the inability of the Napoleon and Lambert pollen to set fruit on the Bing. Black Tartarian. — Chapman, Advance, Bing", Pontiac, and Early Purple are recommended as pollinizers for Black Tartarian in the order named. BLACK REPVBLICA^N CHERRY POLLINATIONS Vaca Valley- California 1916 to 1920 Inclusive Cro55 Percent of Blossoms Maturing AlORMAL SET x5e L P xBlagk Tartarian xBing xEarly Pl/rple xLambert X>NaPOLEO,M xRoGKPORT 19)6 3 tO JO so *0 SO 1317 1918 1919 1920 > t° *0 90 *0 JO ^^ m ^^ ■ ™ I. ■ __._ — Fig. 6. — This chart shows the influence during the seasons of 1916 to 1920, inclusive, of various kinds of pollen when applied to the flowers of the Black Republican variety. Note the failure to set fruit when self-pollinated. BULLETIN 385] POLLINATION OF THE SWEET CHERRY 17 Burbank. — Chapman, Black Tartarian, Black Republican, and Black Heart are satisfactory as pollinizers for the Burbank and are listed in the order recommended. Chapman. — Advance, Black Tartarian, and Black Heart are satis- factory pollinizers for Chapman. Early Purple. — No satisfactory pollinizer has been found for Early Purple. Rockport is inter-sterile with Early Purple. Lambert. — Black Tartarian, Black Republican, and Pontiac are recommended as pollinizers for Lambert. Napoleon and Bing are inter-sterile with Lambert. /NAPOLE07N CHERRY POLLINATIONS VAGAVALLty-CrtLir-OR/NIA-J9l6T0l920 /AICLV/5IVE Cross Percenl of Blossoms Malvring /SormalSqt XSCLP xBl/16 xBlack Repvslican xBlack Tartarian xLambcrt XPo/ITIAC 1316 19 ZO SO 40 $e ■ 1317 » O 10 SO 40 iO ■ 1318 > /0 10 JO 4Q & t ■ 1913 > /a zo jo -jo so . ■ 1920 ? 'O iO JO 40 JO ■ NMH 1 ^■■■^ 1 1 BZB Fig. 7. — This chart shows the influence during the seasons of 1916 to 1920, inclusive, of various kinds of pollen when applied to the flowers of the Napoleon variety. Note the failure to set fruit when self -pollinated; also the inability of the Bing and Lambert pollen to set fruit on the Napoleon. Napoleon. — Black Tartarian, Black Republican, and Pontiac are the most satisfactory pollinizers for Napoleon. Bing and Lambert are inter-sterile with Napoleon. Figure 7 shows graphically the polli- nation requirements of the Napoleon. Pontiac. — Advance, Black "Republican, Lambert, and Napoleon appear to be the best pollinizers for Pontiac. Rockport. — Burbank, Black Republican, and Pontiac appear to be the best pollinizers for the Rockport. The following diagram (fig. 8) represents graphically the varietal requirements of certain sweet cherry varieties. A square indicates crosses which are inter-fertile. A circle indicates self -sterility, or inter- sterility between varieties, and the blank spaces indicate crosses which are not recommended or which have not been made. 18 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Piagramatig Representation or- THE POLLI/NATIO/H REQIREWE/NT5 or GERTAW 5WEET CliERRy VARIETIE5 2; < h y s * z: c 3 S ? J -^ cr h k $ _^ -"" -J > ^ i CQ cQ[Q tfl Q -J IX > _J a C S i s >- iU <* _] c O ^ Cl cx t- s: