Compatibility of scion and stock combinations in Uapaca kirkiana fruit trees has not been evaluated despite noticeable growth irregularities. The objectives of this study were to determine graft compatibility of scion/stock combinations and possible causes of graft incompatibility. Scion, stock, and graft union diameters were measured. Stem sections comprising the graft unions were immersed in formalin acetic acid and then washed in sterile water. These were transversely dissected across the unions and examined under using light microscope. There were considerable growth disorders at the unions, which included significant overgrowth of stocks and unions and constricted unions. There were cracks in the bark across the union in many graft combinations. Anatomic and histological studies showed accumulation of phenol deposits and necrotic tissues, and there was no continuity of vascular tissues above the union. There were also differences in proliferation of callus tissues among grafted partners. Continuity in wood and bark tissues below the unions supported growth of partially compatible partners, whereas isolated parenchymatous tissues at the union supported growth of incompatible partners. There were many necrotic tissues and unfilled areas above the union. Accumulation of phenolic and necrotic cell deposits, poor or a high level of callusing at the union, and possibly specific incompatibility reactions were implicated as the causes of graft incompatibility in U. kirkiana trees.
Simon A. Mng'omba, Elsa S. du Toit, Festus K. Akinnifesi, and Helena M. Venter
Irene Kadzere, Chris B. Watkins, Ian A. Merwin, Festus K. Akinnifesi, John D. K. Saka, and Jarret Mhango
The full commercial potential of wild loquat [Uapaca kirkiana (Muell. Arg.)], a fruit that is widely used for food and income in parts of Africa, is restricted by its short shelf life and variability in postharvest quality. We have evaluated within and among tree variability in fruit size and color at harvest, and changes of color, soluble solids concentrations (SSC) and pulp deterioration during storage, of fruit harvested during the maturation period. The relationships between fruit shape, size, seed number and SSC of fruit harvested at the ripe stage of maturity was also assessed. Size and color of fruit within and among trees at harvest varied greatly within the same location on the same harvest date. The a* values (redness) were more variable than for other color attributes, reflecting a range of fruit colors from greenish to brown. During a 6 day storage period, fruit color lightness and yellowness decreased, while redness increased, and variation in color attributes decreased. Although fruit color intensified during storage, the SSC of fruit after ripening was linked more with fruit color at harvest, with mean concentrations ranging from 6.7% to 13.8% among trees. When fruit were harvested four weeks later and categorized by color at harvest, SSC varied from 11.8% in greenish-yellow fruit to 14.5% in browner fruit. Pulp deterioration of stored fruit harvested unripe was observed by 6 days. The SSC of fruit harvested when ripe was not significantly correlated with shape, size or seed number. These observations have important implications for germplasm selection and collection of U. kirkiana for domestication purposes. Timing of harvest and/or postharvest sorting of fruit is likely to reduce variability in SSC during the postharvest period.
Festus K. Akinnifesi, Simon A. Mng'omba, Gudeta Sileshi, Thomson G. Chilanga, Jarret Mhango, Oluyede C. Ajayi, Sebastian Chakeredza, Betserai I. Nyoka, and France M.T. Gondwe
One of the limitations of Uapaca kirkiana on-farm cultivation is the long juvenile phase to reach a stable fruiting stage. Marcots and grafts have been identified as feasible and reliable propagation methods for precocious fruiting, but the effects of different propagule types on tree growth and fruit yield have not been evaluated. There is limited knowledge on development and growth forms for trees derived from different propagules. Grafts and marcots were compared with saplings to assess the variability in 1) field growth and fruiting of U. kirkiana; and 2) dry matter allocation pattern and tree development models among trees derived from different propagules. Tree development models were used to examine differences among trees from different propagules. The results show that number of branches and fruit load significantly differed between vegetative propagules and saplings, whereas tree height, root collar diameter, crown spread, and fruit size and weight were similar 8 years after establishment. The results suggest differences in intraspecific scaling relationships between height and diameter among propagule sources. Saplings showed a significantly better fit (r 2 = 0.891; P < 0.0001) to the scaling relationship than grafts (r 2 = 0.724; P = 0.002) and marcots (r 2 = 0.533; P = 0.018). After 3 years, marcots and grafts started producing fruits. Fruit load was greatest in marcots despite some fruit abortions; thus, marcots had greater fruit yield, early growth, and development and better dry matter allocation.