Sensitivity of faba bean (Vicia faba L.) cultivars to aphis Fabae scopoli infestation and plant parameters responsible for low susceptibility to the pes

The most economically significant pest of V icia faba L. beans is the bean aphid Aphis fabae Scopoli ( Hemiptera , Homoptera : Aphididae ). The use of varieties resistant to various aphid species can increase the production of this crop, reduce environmental pollution and the cost of monitoring the condition of crops. It is known about the relationship between the degree of damage by aphids and the morphological features of the plant, however, information on chemical changes during damage by aphids and the role of chemical factors in sensitivity to A. fabae is ambiguous. In the present work, for 12 varieties of V. faba from the collection of the Institute of Forage Crops (Pleven), it was shown for the first time that the A. fabae infestation led to a decrease in plant height, crude protein, phosphorus, and chlorophyll a + b while the amount of cyanogenic glycosides increased significantly. Therefore, the aim of the present study was to assess the sensitivity of faba bean cultivars to Aphis fabae and to define the morphological and chemical parameters responsible for low aphid susceptibility. The field study was carried out at the Institute of Forage Crops (Pleven, 2016-2018) in the experiment laid out in Randomized Block Design (RBD). The infestation was assessed by recording the number of aphids per plant at the stages of budding, flowering and bean formation ( n = 20, N = 3), resistance or susceptibility of plants was classified using a 0-12-point scale. The chemical composition (the content of crude protein, phosphorus, chlorophyll a, chlorophyll b, cyanogenic glycosides) was determined by standard methods (Weende system analysis). It was found that aphids reached the highest abundance at the stage of pod formation. Cultivars Fb 3270 and BGE 029055 were defined as very low susceptible to aphids, while BGE 002106, BGE 032012 and BGE 041470 were medium susceptible. Aphid infestation significantly affected the morphological and chemical traits of cultivars and led to a reduction of the plant height, crude protein, phosphorus and chlorophyll a + b content, while cyanogenic glycosides significantly increased in response to aphid injury. The extent of the decrease in chemical parameters and plant height depends on the aphid abundance, being significantly higher in very high susceptible and high susceptible cultivars. On the contrary, cyanogenic glycosides increase with an increase in the aphid abundance. Thereof, the levels of crude protein, phosphorus and cyanogenic glycosides can serve as key factors indicative of the aphid preference. Cultivars Fb 3270 and BGE 029055 with higher phosphorus and cyanogenic glycosides, lower crude protein, and shorter plants had significantly lower aphid infestations. Therefore, these varieties are significantly less susceptible to A. fabae than other varieties and can be involved in breeding programs to improve plant resistance to A. fabae .