Cultivares de algodoeiro herbáceo submetidas à infestação natural de pragas.

Abstract

The cotton cultivars have different morphological and chemical characteristics that may influence the susceptibility of the plants to pests. The objective of this work was to compare the susceptibility of the Upland cotton cultivars BRS Antares, BRS 201, BRS Facual, BRS Ipê, BRS ITA 96, BRS Sucupira, CNPA 8 H, CNPA ITA 90, CNPA Precoce 3 and DeltaOpal to agricultural pests in the conditions of Fortaleza-Ceará, Brazil. In field tests, the experimental design was a completely randomized block with three replications for the plants submitted to natural infestation and one repetition for the plants with control of the infestation. Each experimental unit had three rows with three meters long. The area observation was composed by the central row with thirteen plants. The evaluations of the infestations were made across observations in the field ever each seven days. The number of plants infested by mealybug (Planococcus sp.) and aphid (Aphis gossypii) was recorded each seven days when the plants had at least one colony of the species. The number of plants infested by yellow beetle (Costalimaita ferruginea) was recorded when the plants had at least 10% or more leaves damaged. In the infestation for pink bollworm (Pectinophora gossypiella) it was recorded the number of attacked plants. The following agronomic characteristics were considered: (a) first fruiting branch height, (b) number of nodes for the first fruiting branch, (c) plant height, (d) number of fruiting branches/plant, (e) number of boll/plant, (f) days of first flower open, (g) days of first boll open, (h) average of boll weight, (i) fiber percentage, (j) 100 seeds weight, (l) earliness and (m) yield. In greenhouse test, the plants of the ten cultivars were infested with six adult aphids after six days of germination. The number of adults/plant was recorded twenty four hours after infestation and the number of ninphs and adults/plant was also recorded six days after beginning of the experiment. The experimental design was a completely randomized with six replication of each cultivar. There were no significant differences among the cultivars damaged by Planococcus sp, A. gossypii, C. ferruginea. The cultivars BRS Antares, CNPA Precoce 3 and DeltaOpal were more infested by P. gossypiella than the other cultivars. There were significant differences among infested plants and control plants for the following characters: first fruiting branch height, plant height, earliness, yield and average of boll weight. CNPA Precoce 3 yielded less fibers and CNPA ITA 90 had the highest fiber yield. The greenhouse results indicated that there were no significant differences among the cultivars which showed an average of 4,06 adults twenty four hours after infestation and also 7,76 and 62,91 ninphs and adults respectively, six days after the infestation. CNPA ITA 90 cultivar was the one with smaller susceptibility to pests.