Sue K. Dove

Long-term dichogamy of 80 pecan cultivars

Abstract Data are presented on dates of pollen shed and pistil receptivity for up to 16 years for 80 pecan (Carya illinoensis (Wangenh.) C. Koch) cultivars and selections grown at Tifton, GA, USA. The data are useful for matching cultivars for optimum cross-pollination and minimum self-pollination. Pollination and pistil receptivity dates relative to the industry standard cultivar ‘Stuart’ are given so that the data should be useful at most geographical locations. Mean number of days of overlap of pistil receptivity and pollen shed ranged from 0 to 8 and varied greatly within a cultivar. Dates of pollen shed and pistil receptivity relative to ‘Stuart’ also varied greatly thus indicating that several pollinator cultivars are needed to ensure good cross-pollination every year. The data indicate that actual pollen release and pistil receptivity dates are more important in selecting pollinator cultivars than type of dichogamy.

Pecan Varietal Differences in Hemipteran Kernel Damage

Pecan, Carya illinoensis Wangenh. (K. Koch), is susceptible to feeding by leaffooted bugs (Hemiptera: Coriedae) and stink bugs (Hemiptera: Pentatomidae) from fruit set to post harvest. These hemipterans are difficult to control with insecticide sprays. We found that 33 pecan varieties had consistent and significant differences in the incidence of hemipteran kernel damage indicating that host plant resistance may help solve this problem. The rank of varieties for average incidence of damage over 4 yrs, from highest to lowest was: ‘USDA 53-11-139’, ‘USDA 57-7-22’, ‘Shawnee’, ‘Moreland’, ‘USDA 40-9-266’, ‘USDA 49-20-112’, ‘Linberger’, ‘Cape Fear’, ‘Robinson’, ‘Shoshoni’, ‘USDA 64-11-17’, ‘USDA 55-12-17’, ‘Caddo’, ‘USDA 62-5-8’, ‘Sioux’, ‘Melrose’, ‘Tejas’, ‘Pawnee’, ‘Forkert’, ‘Kiowa’, ‘Owens’, ‘Candy’, ‘Gloria Grande’, ‘USDA 49-1-182’, ‘Western Schley’, ‘Creek’, ‘USDA 53-3-36’, ‘USDA 41-19-20’, ‘Maramec’, ‘Sumner’, ‘GraBohls’, ‘Kanza’, and ‘USDA 53-9-1’. Many of the more tolerant varieties have desirable ke...

Increased Fertilizer Levels Do Not Prevent Abscisic Acid–Induced Chlorosis in Pansy

Abscisic acid (ABA) is a plant hormone involved in regulating stomatal responses to environmental stress. By inducing stomatal closure, applications of exogenous ABA can reduce plant water use and delay the onset of drought stress when plants are not watered. However, ABA can also cause unwanted side effects, including chlorosis. Pansy (Viola ·wittrockiana) has been shown to be particularly susceptible to ABA-induced chlorosis. The objective of this study was to determine if fertilization rate affects the severity of ABA-induced chlorosis in this species. ‘Delta PremiumPure Yellow’ pansy seedlings were fertilizedwith controlled-release fertilizer incorporated at rates from 0 to 8 g L of substrate. When plants had reached a salable size, half the plants were sprayed with a solution containing 1 g L ABA, whereas the other plants were sprayed with water. Leaf chlorophyll content was monitored for 2 weeks following ABA application. Leaf chlorophyll content increased greatly as fertilizer rate increased from 0 to 2 g L, with little increase in leaf chlorophyll at even higher fertilizer rates. ABA induced chlorosis, irrespective of the fertilizer rate. Plant dry weight was lowest when no controlledrelease fertilizer was incorporated, but similar in all fertilized treatments. ABA treatment reduced shoot dry weight by 24%, regardless of fertilization rate. This may be due to ABA-induced stomatal closure, which limits carbon dioxide (CO2) diffusion into the leaves. We conclude that ABA sprays induce chlorosis, regardless of which fertilizer rate is used. However, because leaf chlorophyll concentration increases with increasing fertilizer rates, higher fertilizer rates can mask ABAinduced chlorosis.