Abstract
Phenology study was conducted to assess 22 genotypes of Sclerocarya birrea (A. Rich.) Hochst, collected from West, Eastern and Southern Africa. Assessments were done on time for bud onset, flower opening, leaf flush, fruit set, fruit maturity period and fruit production. Highly significant (P< 0.001) variations between provenances were obtained in all the phenological traits assessed including variations between sexes in time from flower bud set to anthesis. There was flowering overlaps and synchrony between provenances and sexes with males flowering earlier than females. So far two subpopulations have emerged within the trial referred to as early and late flowering genotypes. The early flowering included provenances from Mozambique, and Swaziland while the late flowering encompassed provenances from Malawi, Zimbabwe, Namibia, Tanzania and Zambia. Fruit maturity period ranged from 76±2 to 192±15days. The early flowering genotypes flowered, fruited and matured between August and January while the late genotypes flowered and fruited from September to May. There were highly significant (P≤0.001) variations in fruit yield of S. birrea provenances between 2016/2017 and 2017/2018 seasons with the former being more productive than the later confirming that S. birrea fruit yield is not constant across seasons due to seed mating effects. There were very strong positive relationship ranging r=0.81 to r=0.78 between leaf flush, bud set, flower opening and fruit set significant at (P<0.001). Some trees classified as females in the first year as based on flowers were found have male flowers which calls for more detailed investigations into this sex change behaviour.
Highlights
In order to study the phenology of S. birrea we aimed to answer the following questions: (1) Do all the geographic populations have the same flowering time and length of flowering? (2) Are there variations between populations in time for bud set, flower opening, leaf flush and fruit set? (3) Do variations exist between sexes from flower bud set to anthesis? (4) Is there flowering synchrony between male and female trees? (5) Does provenance vary in the duration for fruit maturation? (6) Are there variations in fruit productivity between seasons?
4-1- Variations in Time for Bud Set to Flower Opening (Anthesis) The results of this study have shown wide variability between provenances of S. birrea in bud set to anthesis with an extended flowering period of about 57 days starting from August and ending October
The results suggest that variations in flower bud set to anthesis may either be due to origin of S. birrea provenances or genetic because the genotypes are sharing same environmental conditions
Summary
An international provenances trial of 22 genotypes of Sclerocarya birrea was established in Mangochi in 1999 to evaluate growth, tolerance to pest and diseases, adaptability (survival), fruit productivity and quality in order to select genotypes with superior traits and well adapted to local conditions for the domestication. The timing of flowering phenology within and between populations is of fundamental biological importance because of. The information on the phenology of S. birrea genotypes is pertinent for successful selection for domestication and breeding program [14]. It is important in assessing barriers to seed and fruit set [15]. (2) Are there variations between populations in time for bud set, flower opening, leaf flush and fruit set? In order to study the phenology of S. birrea we aimed to answer the following questions: (1) Do all the geographic populations have the same flowering time and length of flowering? (2) Are there variations between populations in time for bud set, flower opening, leaf flush and fruit set? (3) Do variations exist between sexes from flower bud set to anthesis? (4) Is there flowering synchrony between male and female trees? (5) Does provenance vary in the duration for fruit maturation? (6) Are there variations in fruit productivity between seasons?
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