Effects of moderate drought conditions on green leaf number , stem height , leaf length and tuber yield of potato cultivars

Our objective was to define sensitive morphological indicators that could be used to discriminate between drought sensitive and drought tolerant potato cultivars before final tuber yield is reached. A total of six potato cultivars contrasting for drought tolerance and earliness were subjected to three levels of water supply in two field trials in 1995 and 1996. We examined which parameter among stem height, number of green leaves and leaf length (the two latter parameters were only measured on two cultivars) was most sensitive to moderate drought conditions and responded similarly to water shortage regarding tuber yield, tuber number and average tuber dry weight. Drought reduced the number of green leaves in cultivars Krostar and Désirée, respectively, up to 22 and 25% 124 days after planting during the season but this effect levelled off towards the end of the season. Drought also induced significant length reductions (29, 43 and 53%, respectively, for the leaf numbers 17, 18 and 19) but there were no differences among the two cultivars examined. Stem height was sensitive to drought and the effect was stronger on later cultivars especially when water shortage started early as in 1996. In 1996, stem height ratios were negatively related (R=0.80) to TDWS (tuber yield ratio indicative of drought tolerance) whereas they were positively related in 1995 (R=0.21). However, care is needed as the negative relationship of 1996 was associated to earliness of cultivars. Indeed, stem height was less reduced in early cultivars (13 and 14% for Eersteling and Jaerla, respectively) than in mid-late cultivars (25 and 29% for Désirée and Nicola, respectively). In the drought treatment, no supernumerary tuber was observed across the season contrary to the irrigated treatment. According to the year, final tuber number or average tuber dry weight was reduced by the drought treatment. Reduction in tuber number (17%) in the drought treatment was not associated to lower tuber yields due to compensation by average tuber dry weight (6%). Different growth strategies can be followed by the potato plant to adapt to different drought conditions without tuber yield being significantly affected. © 2001 Elsevier Science B.V. All rights reserved.