Inheritance of tolerance to drought from selected potato (Solanum tuberosum) cultivars in Uganda
Kesiime, Vasiter Eunice
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Potato is one of the important staple foods and source of income in the highlands of Uganda. However, its production is being affected by fluctuation in precipitations in both timing and amount, resulting into drought and reduced potato productivity. Many regions in the world that previously had stable and reliable rainfall patterns, particularly in tropical highlands currently suffer from intermittent droughts. This is primarily attributed to global warming. Also, in Uganda the area of substantial potato production is expanding into locations at lower altitudes, where drought is more common. Therefore, drought stress mitigation measures and coping mechanisms need to be devised to face future challenges of climate change particularly in developing countries. This study therefore, aimed at describing the mechanisms of inheritance of drought tolerance in Ugandan potato varieties that will help develop breeding materials that are tolerant to drought and potential to provide acceptable yield in both quantity and tuber quality. A green house experiment was conducted twice at Kachwekano Zonal Agricultural Research and Development Institute (KAZARDI) from October, 2011 to February, 2012 and April 2012 to July 2012 to evaluate and characterize eight potato genotypes; five of which were obtained from CIP (international potato center) breeding collection for drought tolerance, and three local varieties in Uganda with unknown reaction to drought. The experimental materials were tested for drought tolerance at three levels of simulated moisture deficit. The moisture deficit treatments were to maintain the moisture level at full field capacity, 50% field capacity and 25% field capacity. The moisture deficit levels constituted the main plot while the clones comprised the subplot. The treatment combinations were repeated four times. Data was collected on leaf chlorophyll content, relative leaf water content, number of days to 50 percent flowering, percent ground cover, leaf area, plant height, number of stems per plant, stem diameter, stress score, increment in plant height after imposing stress, dry matter content and yield components. Analysis of variance for effect of watering regime against eight potato genotypes indicated that potato genotypes performed significantly different (P≤ 0.05) for all the traits evaluated, in both repeats. Results from both growth, physiological and yield parameters revealed that the new potato clones bred for drought tolerance were less affected by drought stress compared to adapted varieties. Kachpot1 gave the least stress score (1, 2.4 and 3.9) followed by Clone 395017.242 (1, 2.4 and 3.9) in the plots watered to field capacity, half and quarter field capacity respectively. The overall mean yield reduced from 21 tons per hectare in well watered plots to 12.5 in 50% moisture stressed plots and 10 tons per hectare in 25% moisture stressed plots. The highest yield under 25% moisture stress was obtained from clone 394034.7(12.6 tons per hectare), followed by 391533.1 (11.1) and 393077.159 (10.9). Percent yield reduction from normal watering to severe stress was least in clone 391533.1 (38.5%), followed by 394034.7 (39%), and 395017.242 (49.6). Four best performing clones under moisture stress were crossed with three susceptible varieties in North Carolina 2 design generating 12 progeny families in order to determine the combining ability. Analysis revealed that parents 391533.1 and 395017.242 were the best combiners for most of the traits implying that they can be used to breed and select for cross combinations with tolerance to drought. Relative importance of GCA to SCA was high based on baker’s ratio for % dry matter content (0.8), leaf area (0.7), plant height (0.6), relative leaf water content (0.5), stem diameter (0.6), groundcover (0.5) and total number of tubers (0.6), implying that the relative contribution of additive gene action for these traits is high compared to the non additive gene action. This suggests that these traits are highly heritable and selection can be done in early generations to develop varieties tolerant to drought. Also broad sense heritability was high for most traits than the narrow sense heritability implying low environmental effects in the overall phenotypic expression of the observed traits.