Adaptive Germination Responses by Walnut (Juglans) Pollen to Temperature during Pollen Development

Abstract

Pollen was collected from 10 cultivars and clones of Juglans regia and 3 of J. nigra and germinated at a range of temperatures. For both species maximum tube growth occurred at 32-33°C except for J. regia cv. Manregian where it occurred at 29°C. Only pollen from early flowering cultivars (Serr, Manregian, Early Erhardt) germinated at low temperatures (14-15°C). Branches of cv. Serr containing staminate inflorescences were subjected to several temperature regimes to determine whether time of male flowering and adaptation to temperature by pollen are manifestations of genetically fixed responses by the male gametophytes to temperature conditions prevalent at pollen dispersal or whether they are a phenotypic response to these conditions. The results indicate that there is a plastic component of the in vitro pollen germination response to temperature that is partially affected by the environment during the pollen development period.