Factors Influencing Fruit Setting in the Pecan

The pistillate flower of the pecan consists of an orthotropous ovule, surrounded by a single integument. The portion which becomes the shell consists of two carpels, which are transverse on the axis of the inflorescence. The 4-valved husk is developed from the lower portions of the calyx lobes. The flowers are sessile on the peduncle, and are borne in clusters usually of two to six. 2. The pollen tube grows down through the style and ovary wall or integument to the base of the ovule, and returns through the chalaza and nucellus to the embryo sac, fertilization occurring about 4 weeks after pollination. 3. There is a definite drop of young nuts about 4 weeks after the time of pollination, and this drop accounts for over 75 per cent of the seasonal drop. It appears to be due to lack of pollination. 4. The varieties tested show no evidence of self-incompatibility or inter-incompatibility. Good sets of fruit were obtained from any variety of pollen available when the flowers were receptive. 5. The period of maturity of staminate and pistillate flowers of the pecan do not often coincide. This condition of dichogamy may be complete or incomplete, and the special type may be protandry or protogyny. Some varieties, such as Moore, Alley, Texas Prolific, and San Saba, have been protandrous every season, and have had pollen available in time to pollinate the earliest flowers of any variety. Some varieties, especially Moneymaker, Bolton, and Success, have been protogynous or overlapping slightly every year, and have been dependent upon other varieties for pollination in almost every case. A group of varieties, including Delmas, Burkett, Schley, and Stuart, which are frequently recommended for planting together, have been protandrous or overlapping only two years in five. These leading varieties in Texas need other varieties near them to insure availability of early pollen. 6. Certain seasons have been favorable to protandry and others to protogyny. The data on temperature and rainfall for the spring seasons indicate that moisture and high temperature in this period favor early maturity of the staminate flowers, and cool, dry seasons favor earlier maturity of the pistillate flowers. The warm seasons of heavier rainfall advance maturity of both the staminate and pistillate flowers, but the staminate flowers of any one variety are less variable in their requirement of heat units. 7. It may be said that the early dropping of fruits in the pecan is due primarily to lack of pollination, and this, in turn, is due to dichogamy. Certain varieties (Moore, Alley, Texas Prolific, and San Saba) have proved to be reliable in the production of pollen at an early date, and some of these varieties should be used in every pecan orchard.