The competitive ability of different chickpea (Cicer arietinum) genotypes against Polygonum aviculare under fiald conditions

Polygonum aviculare L. is a troublesome weed in chickpea cultivated in theMediterranean environment of Central Italy. A 2-year field studywas carried out to evaluate the competitive ability and the yield response of different chickpea genotypes against P. aviculare. Experimental treatments consisted in six chickpea genotypes (Alto Lazio, C1017, C133, C134, C6150 stable lines and cultivar Sultano) cultivated in weed-free conditions and with P. aviculare at four densities (4, 8, 16, 32 plants m2). The competitive ability of chickpea against P. aviculare was assessed on the basis of (i) the relative biomass total (RBT); (ii) the competitive balance index (Cb), and (iii) the competitive index (CI). The chickpea seed yield in weed-free conditions ranged from 2.6 to 2.1 t ha1 of DM and was higher in C6150 and Sultano. P. aviculare caused an average chickpea seed yield loss of 14, 46, 74 and 88% at the density of 4, 8, 16, 32 plants m2 compared to the weed-free crop. The relationship between the P. aviculare density and the percentage of chickpea yield losswas described by the rectangular hyperbola model with the asymptote constrained to 100% maximum yield loss. The estimated coefficient I (yield loss per unit density as density approaches zero) was lower in C133, Sultano, and C1017. RBT was higher than 1 in all chickpea genotypes at 4 plants m2 of P. aviculare, while at higher P. aviculare densities it was similar to 1 suggesting that there is no resource use complementarity between chickpea and the weed. Generally, at the density of 50 plantsm2 the chickpea cropwas more competitive than P. aviculare at 4 plants m2 (Cb > 0), equally competitive at 8 plants m2 (Cb ¼ 0), and less competitive at 16 and 32 plants m2 (Cb < 0). No chickpea genotype achieved the objective of combining a high seed yield potential and a great competitive ability against P. aviculare. C6150 and Sultano had a high seed yield production in weed-free conditions, but they were poorly competitive against P. aviculare at intermediate and high weed infestation, while C1017 showed a satisfactory level of Cb and CI at all P. aviculare densities although its seed yield was the lowest in weed-free conditions. However, the results suggest that, from an agronomical point of view, P. aviculare plant density should be less than 4 plant m2 in order to prevent severe chickpea seed yield loss in field conditions.