Resistance of sweet pepper genotypes to abiotic stresses in growing conditions of low-capacity hydroponics

The modern trend of vegetable crop breeding is a development of new cultivars and hybrids resistant to abiotic and biotic stresses and suitable for fully mechanized agriculture. It can provide the maximal commercial output and high profitability of vegetable growing. Pre-breeding is based on knowledge of impact of various abiotic factors on the yield and productivity of certain genotype in specific growing conditions. Traditionally the pepper plants are cultivated in greenhouses on low-volume soil or artificial medium with drop irrigation. Main advantage of low-volume technologies is a labor saving and improved phytosanitary conditions. In the present paper, the response of different sweet pepper ( Capsicum annuum L.) genotypes to various abiotic factors has been studied aiming at development of initial breeding material for new varieties and hybrids under the hydroponic system conditions. The investigation has been conducted in 2008-2014 in the All-Russian Research Institute for vegetable breeding and seed production (Moscow Province). The breeding and collection samples of sweet pepper as well as F1 hybrid Raisa (standard) were used in the present study. Plants were grown in a greenhouse on sphagnum peat mixed with calcified substance as a potting substrate and mineral fertilizers. The concentration of nutrient solution for irrigation of seedlings conforms to the recommended standard. The growth conditions were partially controlled. The parameters of outside environment were recorded during growing period using an automated climate control system KISTOCK KH-100 (France). The soil temperature was also controlled. Yield sample characteristics and assessment were done by UPOV system (Union Internationale pour la protection des obtentions végétales, France). The most adverse factores were recorded in the beginning (February-May) and the end (September-October) of growing season regardless of year of investigation, that resulted in decreasing marketability of the yield. The unmarketable part of yield was represented by fruits with excessive growth, deformation, and affected by blossom-end rot. Long-term screening of pepper genotypes on responsiveness to unfavorable factors of environment allowed to divide the cultivars into the following groups: susceptible (cv. Agapovskii), low-susceptible (cv. Elisa), and tolerant (cv. Zheltiyi buket). At hydroponics, productivity of the susceptible cultivar Agapovskiy was decreased up to 40 % as compared with the tolerant cultivar Zheltiyi buket. It was shown that adaptability of sweet pepper varieties to the conditions of low-capacity hydroponics is defined by the norm of reaction to changes of environmental factors such as daily temperature, difference of night and day temperatures, humidity, and its combinations. Changes of the light intensity is not so crucial for cultivars productivity; it may have negative impact on varieties with low adaptability when combined with other environment parameters. The correlation between the rate of non-standard part of yield, the damage of fruits caused by blossom-end rot, and the microclimate parameters differed among the varieties. Development of non-standard fruits in the susceptible and the low-susceptible cultivars is due to low humidity (at r value ranged from -0.65 to -0.72), while in the tolerant cultivars it depends on a big difference between the day and night temperatures (at r > +0.70). Damage of fruits caused by blossom-end rot is more genotype dependent. In all genotype, it is promoted by huge temperature changes, being stronger related to this factor in the susceptible genotypes at r = 0.65-0.75. For development of new pepper varieties and hybrids suitable for low-capacity hydroponics, the initial breeding material with high norm of reaction to temperature and high resistance to low humidity must be selected.