Yield and morphological responses of twenty potato (Solanum tuberosom L.) genotypes in response to drought stress

Water deficit poses severe limitation to potato cultivation as a drought-sensitive crop plant. Selection of tolerant genotypes based on a combination of tolerance indices can provide useful criteria for breeding drought tolerant potato varieties. Water deficit affects plants at various levels and stages of their life cycle. This abiotic stress not only affects plant–water relations through the reduction of leaf water content, turgor, and total water, but it also affects stomata closure, limits gas exchange, reduces transpiration, and disturbs photosynthesis. In potato, tolerance to drought is a very complex trait. Photosynthesis is one of the basic physiological processes of plants with internal and external conditions. Any reduction of the intensity of this process causes a decrease in the amount and quality of crop plants. One of the indicators for early prediction of potato yielding can be the measurement of chlorophyll content. It is an informative tool for studying the effects of dif ferent environmental stresses on photosynthesis.  Chlorophyll content has an important role in photosynthesis and in understanding plant functions.  In any research, measuring of the chlorophyll content is used for assessment of potato genotypes tolerant and/or sen sitive to environmental stresses.

In this study, 20 potato genotypes were evaluated under two water levels; normal and water deficit stress conditions. The experiment was performed as spilt-plot based on randomized complete block design with three replications at the Seed and Plant Improvement Institute, Karaj, Iran in 2018. The correlations among the different traits were measured and estimated by calculating Pearson correlation coefficients using the statistical tool in Minitab 17. Tuber yield, yield components, growth parameters, and morphological traits were measured under both well-watered and water stressed treatments. Morphological and reproductive characteristics such as plant height, leaf dry weight, chlorophyll content, yield tuber, ware yield, seed yield, non-marketable yield, and marketable yield were measured. 

Analysis of variance showed that stem number, chlorophyll content, stem thickness, plant height, leaf dry weight (LDW), total yield, ware yield (yield>55 mm), seed yield (yield 35-55 mm), non-marketable yield (yield<35 mm), and marketable yield (ware and seed yield) were significantly affected by genotype and drough and their interaction. Analysis of variance showed that the simple effect of genotype treatment on all studied traits including yield, ware yield, seed yield and marketable yield, LDW, stem thickness, plant height, chlorophyll content, and stem number were significant at 1% level. Correlation of stem number and plant height was highly positive and significant at the 0.01 level. Principal component analysis (PCA) and measured traits showed that genotypes 2, 5, 7 and 13 had high performance in the studied stress environment. To fully reflect the various factors that played a principal role in the comprehensive indicators, PCA was carried out on quantitative traits. The accumulative contribution rate accounted for 99% of the total variation for PC3. Analysis of PCA by the correlation matrix and the biplot analysis methods used in this study revealed that these parameters could be used for evaluating the responses of potato genotypes to water deficit in different environments.  The associations among traits related to yield and genotypes are graphically revealed in a biplot of PC1 and PC2. The PC1 and PC2 axes mainly distinguish the morphological traits and yield-related traits in three different groups.   

Parameters related to yield and leaf photosynthetic pigment content (chlorophyll content) were used to rank the clones and cultivars tested for comparative analysis. Based on our results, genotype 7 performed well under normal and water stress conditions. Water deficit is an important constraint limiting the crop productivity worldwide. Plants show a wide range of responses to water deficit which are mostly expressed by a variety of alterations in the growth and morphology of plants. Field experiments revealed that water deficit affects all evaluated morphological and yield related traits.