Factors affecting yield in cashew (Anacardium occidentale L.)

Abstract

Investigations on the different vegetative, flowering and fruiting characters, influencing yield in cashew, were undertaken at the main campus of Kerala Agricultural University at Vellanikkara. These studies were made during the period from November 1978 to April 1979. Important vegetative characters studied were the percentage of flowered shoots per unit area of tree canopy and the growth parameters of the tree represented by spread and height. The major flowering and fruiting characters studied were the pattern of flower opening, percentage of bisexual flowers, factors affecting pollination, fruit-set, fruit-drop and the mean weight of nuts harvested. The results showed that among the vegetative characters, percentage of flowered shoots per unit area of tree canopy was found to be the most important factor, contributing to yield. Tree-spread was also found to have a positive correlation with yield. The influences of this character on yield was not direct but indirectly through the former character. There was no significant correlation between yield and height of the tree. Pattern of flower opening in cashew panicles was found to have three phases viz., the first male phase followed by a mixed phase which is again followed by a second male phase. The duration of these three phases was found to be varying in the different trees. It was found that some trees had only the mixed phase throughout and those trees yielding above the median had a longer mixed phase as compared to the trees yielding below the median. A positive correlation was found between yield and percentage of bisexual flowers in the tree. Among the flowering and fruiting characters affecting yield, this factor was found to influence yield much more than any other character. Examination of a random number of bisexual flowers revealed that a large proportion of bisexual flowers remained unpollinated in nature. So, lack of pollination was found to be one of the reasons for poor fruit-set and yield in cashew. This was further confirmed from the high fruit-set obtained in the hand pollinated panicles. Receptivity of the stigma was found to be continuing up for 48 hours after flower opening and hence it was not a limiting factor for securing high yield. Supplementing the natural pollination with the help of insect pollinators met with some success. Keeping bee-hives in the orchards during flowering season is advisable for facilitating better pollination. A positive correlation could be observed between yield and percentage of fruit-set but the ultimate yield was found to be adversely affected by the severe shedding of young fruits before reaching maturity. The intensity of fruit-drop was found to be high in the early stages of development but it declined during the later stages. The causes of fruit-drop that could be identified were those resulting from the attack of insect pests, adverse climatic conditions etc. Studies did not reveal any significant correlation between yield and mean weight of nuts harvested.