Evaluation of potato germplasm for warm climate at low elevations in Uganda

Several experiments on Solanum potato were conducted at 0.28 degrees N latitutde and 1250 to 1300m a.s.l in Uganda. Selected genotypes and breeding lines representing a broad genetic base were grown during both long and short rainy seasons from 1989 to 1994 to study their growth and yield response in a warm climate. The genotype differed significantly for all parameters measured except the number of stems plant. High yielding genotypes indicated ability of seed to survive and emerge quickly under high soil temperature and, begin, early and balanced haulm growth with good leaf canopy. Leaf area index varied from 4 to 6 while harvest index ranged from 52.0 to 55.0. Average fresh tuber weight at both harvesting, 67 days after planting, and at full maturity demonstrated that tuber development was faster resulting in their high tuber yield. Conversely lower yields in genetypes unadapted to the mid-altitutde was related to low plant survival and gappy plant stand. The plants grew taller and developed smaller leaflets. Plant growth was undetermined which stimulated the production of small tubers. Genotypes CIP-382171.4, CIP-381381.20, CIP-381379.9, CIP-379706.34 (LT.9) were outstanding in their ability to produce relatively high yields with better average fresh tuber weight. Accessions CIP 800938 and CIP 720108, though having high glyco-alkaloid and high rate of pathological degeneration, respectively, are heat tolerant and high yielding and are potentially valuable for a breeding programme. All high genotypes and Cruza were observed to have useful degrees of resistance to bacteral wilt. There was also strong evidence that genotypes CIP 382171.4 and CIP 381381.20 possess combined resistance to late blight and bacterial wilt. Intensive research is needed on agronomic and physiological problems inherent in potato cultivation under stress conditions (heat and drought)