CULTIVAR BY ENVIRONMENT INTERACTION OF COCONUT UNDER DIFFERENT WATER AND HEAT REGIMES AT THEIR EARLY STAGE OF GROWTH

Four coconut hybrids (brown dwarf x Sri Lanka tall, Sri Lanka tall x brown dwarf, green dwarf x San Ramon and green dwarf x Sri Lanka tall) arising with two parental dwarf coconut varieties; green dwarf and brown dwarf were evaluated for their early vegetative growth and for duration to reproduction at two sites; Raddegoda and Wanathawilluwa. At Raddegoda, a site with optimum condition for growth of coconut, the overall leaf production rate was 9.4 leaves per palm per year during the first 3 year period. In contrast, at Wanathawilluwa, a site subject to severe and prolong drought and heat stress produced 11.3 leaves per palm per year. Moreover, at Wanathawilluwa crosses made with green dwarf produced a remarkably higher number of leaves compared to crosses made with brown dwarf. However, this trend was not noticeable for stem girth indicating that the higher photosynthetic assimilates in green dwarf crosses resulting from higher leaf area were not used for stem growth. When time to attain reproduction is considered, the crosses made with green and brown dwarfs were similar at Raddegoda (43.2 Vs 43.8 months). However, green dwarf crosses at Wanathawilluwa were markedly precocious attaining early maturity (33.25 Vs 41.9 months), but resulting in a large number of stunted palms. This situation was severe in green dwarf x San Ramon. The overall results suggested that early vegetative phase of coconut hybrids resulting from green dwarf parent is more susceptible to drought and heat stress conditions. This phenomenon indicated a differential physiological response of different coconut cultivars under moisture and heat stress.