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Preharvest germination (viviparity) can be a problem with nuts of pecan ( Carya illinoinensis (Wangenh.) K. Koch). Two southern-adapted cultivars ('Cherokee' and 'Wichita') and one northern-adapted cultivar ('Johnson') were paternal parents in controlled crosses with the maternal parent 'Wichita'. 'Wichita' x 'Johnson' seed took much longer to germinate than seed from either the 'Wichita' x 'Cherokee' cross or the 'Wichita' self, therefore indicating that pollen source may influence germination charac- teristics. 1928, 1935; Swingle, 1928); keeping quality (Nebel, 1936); and shell splitting (Whitehouse et al., 1964). "Northern" pecan cultivars are adapted to a shorter growing season (160 to 180 days) as compared to 190 to 220 days for "southern" cultivars (Malstrom et al., 1978). Also, Mad- den and Tisdale (1975) reported that chilling and stratification were needed to after-ripen seeds of some northern cultivars; although after-ripening was not necessary, it promoted the rate of germination. Conversely, most southern cultivars will easily germinate with- out stratification. This difference raises the possibility that northern cultivars (those with parentage from the northern portion of the natural range of pecan) are relatively resistant to viviparity. This northern-southern relation- ship suggests genetic control over viviparity. Such control of viviparity has been shown in Arabidopsis thaliana L. to occur via a single gene that minimizes abscisic acid (ABA) pro- duction in the developing embryo (Karssen, et al., 1983). Endosperm (maternal) ABA was not closely related to the phenomena, whereas embryo ABA (regulated by both the female and male genome) was closely related to pre- mature germination. Therefore, Bruce Wood (personal communication) postulated that a) similar mechanisms are likely to occur in other plant species; b) pecan pollen from northern genotypes (as compared to southern) are more likely to possess genes that act to maximize ABA in embryos because of strong selection pressure against seeds in which dormancy could be prematurely satisfied (this selection pressure would likely be much less intense in southern germplasm); and c) in general, fer- tilization with northern pollen would act to reduce the occurrence of viviparity via en- hanced embryonic ABA levels. This study therefore presents data supporting the hypoth- esis that viviparity can be regulated by pollen source.

A Northern Pecan Pollen Source Delays Germination of Nuts from a Southern Pecan Cultivar