Response of potato genotypes to production sites and water deficit imposed at different growth stages.
Mthembu, Sizwe Goodman.
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In South Africa, potato is an important food security crop widely cultivated by smallholder farmers due to its extensive adaptation characteristics. However, drought adaptive responses of potato genotypes vary under different environmental conditions. Potato is generally categorized as the most sensitive crop to water deficit than other root and tuber crops. However, there is insufficient evidence regarding adaptive responses of potato genotypes to water deficit imposed at different growth stages. Therefore, this study sought to identify growth stage-specific drought adaptation of selected potato genotypes for recommendation and cultivation in targeted production sites in South Africa. The specific objectives of this study were: (1) to determine morpho-physiological traits related to water use efficiency among selected potato genotypes subjected to water deficit at the different growth stages; (2) to determine the effect of water deficit imposed at different growth stages on yield performance and tuber quality of selected potato genotypes; and (3) to investigate the effect of different production sites/regions on growth, physiological and yield responses of potato genotypes. For objective 1, a glasshouse study was conducted using a 8×4×2 factorial experiment involving the following factors: potato genotypes - 8 levels (Bikini, Challenger, Electra, Mondial, Panamera, Sababa, Sifra, and Tyson); growth stages - 4 level (vegetative stage, tuber initiation, tuber bulking and maturity) and watering regimes - 2 levels (Well-watered [Ww] and Water deficit [Wd] conditions). The treatments were replicated three times to give a total of 192 experimental units. Water deficit was imposed by withholding irrigation at the beginning to the end of each growth stage. A highly significant (p < 0.001) interaction among genotypes, water condition and growth stages was observed for morphological traits and physiological responses including number of leaves and total above-ground biomass, and photosynthetic rate (A), instantaneous water use efficiency (IWUE), transpiration rate (Tr), chlorophyll content index (CCI), and relative water content (RWC). Potato genotypes Bikini, Challenger and Mondial with growth-stage specific drought adaptation were identified and recommended for water-limited environments. The second study (objective 2) determined the effect of water deficit imposed at different growth stages on yield performance and tuber quality of selected potato genotypes. The study was conducted as 8×4×2 factorial experiment (See objective 1) replicated three times and data was collected on tuber yield (TY), number of tubers (NT), tuber size distribution (TSD) and dry matter content (DMC). Results revealed a highly significant (p < 0.001) genotype x water condition x growth stages interaction for tuber yield and dry matter content. Imposing water deficit at the tuber initiation and tuber bulking stages resulted in significantly lower yields, whereas drought stress at maturity stage resulted in high number of small tubers. ‘Bikini’, ‘Challenger’, ‘Mondial’ and ‘Tyson’ were identified as tolerance genotypes to water deficit at vegetative stage, tuber initiation and maturity stage due to high yield potential and DMC. This finding suggests that these genotypes could be suitable for processing industry (chipping) and baking. For objective 3, eight potato genotypes were grown across two environments namely: Ukulinga research farm (URF) in Pietermaritzburg which characterised with semi-arid environment and eChibini area (CB) in Bamshela with seasonal rainfall and high humidity. The experiments were laid out using a randomised complete block design (RCBD) replicated three times. Data was collected on morphological and physiological traits. Significant (p < 0.05) genotype x environment interaction effect was observed for studied traits at URF and CB. Potato genotypes planted at CB had a significant (p < 0.05) lower gs and Tr resulting to low A, than at URF. The CCI at CB compared to URF was significant (p < 0.05) higher at the beginning and gradually decreased towards maturity while at URF was constant. Moderately to poorly drained soils at eChibini resulted in low yields and low dry matter content. Various genotypes with better yield and high quality were obtained at URF. This suggested that genotypes were suitable for production in cool temperate regions with humid climate areas like URF. The study showed that different production regions can significantly affect the potato yield performance, suggesting URF sites as suitable environment. Overall, the study identified potato genotypes with growth stage-specific drought tolerance and environment specific adaptation for high yield and good quality.