ECO-PHYSIOLOGICAL FACTORS AFFECTING GROWTH AND DEVELOPMENT OF Calotropis procera IN THE SEMI-ARID REGIONS OF THARAKA AND MAKUENI, KENYA

Abstract

Textile industry faces fibre supply deficit that can be filled by fibre from C. procera. However, current calotrope fibre supply is unsustainable because it is collected from the wild with inadequate information on its growth conditions. Therefore, this study investigated proximate eco-physiological factors affecting C. procera’s growth in its natural habitats for better site matching and domestication. Specifically, the study determined; 1) edaphic and weather conditions in Tharaka and Makueni, 2) morphology, 3) size distribution, 4) phenology and 5) dieback condition of C. procera in Tharaka and Makueni at different time points. Repeated measure and factorial research designs were used. Purposive and simple random sampling techniques were used in selecting blocks with naturally growing C. procera and marking (20 x 20) m permanent plots respectively. Edaphic factors were assessed using soil chemical analysis while weather conditions were obtained from National Aeronautics and Space Administration satellite. Morphology was assessed using leaf surface area, leaf colour and fruit volume. Size distribution entailed measuring shrub’s height, crown and root collar diameters. Phenology entailed estimating activity indices, number of flowers and fruits and phenophase intensities. Dieback condition was assessed through prevalence, severity and causative agents. Data was analyzed using factorial analysis of variance (ANOVA), mixed repeated ANOVA, Kruskal Wallis, Friedman, ordinal regression and generalized estimation equation. Results indicated that soil phosphorus in Tharaka and Makueni were 4.84 ppm and 10.76 ppm respectively at (20-40) cm soil depth. Average monthly rainfall and temperatures were (45.27 - 160.37) mm and (24.92 - 28.78) °C respectively. The volume of between 58.05% and 76.4% of fruits was < 100 cm3. Relative frequency of C. procera stems in (1.5-<3) m height class in Tharaka and Makueni were 44.98% and 69.91% in (June-August) 2018 respectively. The lowest fruiting activity index of 42.71% and 43.64% for Tharaka and Makueni respectively were reported in (September-November) 2019. The highest dieback prevalence of 76.59% and 80.53%, and severity index of 3.56 and 3.42 were reported in Tharaka and Makueni in (September-November) 2019 respectively. Fusarium Fungi was the dominant dieback causative agent with 32.29% – 43.38% dominance. There were significant differences in fruit volume class distribution, size class distribution, activity index, dieback prevalence and severity between research time points (P < 0.001). There were significant associations between C. procera’s growth with soil nitrogen, phosphorus, potassium, average monthly rainfall and temperature. In conclusion, eco-physiological conditions of Tharaka and Makueni favour growth and development of C. procera