Efeito da desfolha simulada sobre a produção de folhas e frutos em cultivares de mamona (Ricinus communis L.), na perspectiva da criação do bicho-da-seda eri (Philosamia ricini Drury, 1777)

Abstract

The effect of simulated defoliation on seed and leaf biomass production of castorbean cultivars was studied aiming to rear erisilkworm Philosamia ricini (Drury, 1777) (Lep.: Saturniidae). The experiment was carried out in the `Campus' of the Federal University of Ceara in Fortaleza, Ceará, Brazil, during the 1999/2000 season. It was used an entirely randomized block design with four replicates in a 5 x 4 factorial model. The five castorbean cultivars were submitted to defoliation at 60, 90, and 120 days after germination, removing 20% of leaves found in the upper portion of plants and 60% in the lower portion. Data relative to leaf biomass and seed productivity were submitted to ANOVA by F test and means were compared by "a priori" orthogonal contrast and Tukey test to 5% significant level. The results were: a) only leaf biomass removing at defoliation, total leaf biomass, and 100 seeds weight were affected by defoliation ages; b) the northeastern cultivars showed greater leaf biomass and seed productivity than southeastern cultivars; c) Removal of 20% of leaves from the upper part of the plant and 60% from the lower, at 60, 90 and 120 days after germination, do not affect seed productivity of cultivars tested; d) Due to the different rhythm of foliage development in castorbean cultivars, specific strategies are required to manage leaf use in erisericulture to maximize its performance: the `Guarani', `IAC-80', `Sipeal 28' and `SM4' cultivars are recommended to defoliate 120 days after germination. For 'BRS-149 Nordestina', there is the need to split the cropped area in 3 parts to defoliate the plants at 60, 90 and 120 days, and also to use the leaf biomass available at final harvesting of fruits; e) The `BRS-149 Nordestina' have the best performance to erisericulture; 1) Because `SM4' is as productive as 'BRS-149 Nordestina', similar production of leaf biomass can be obtained through a specific management of its leaf system, by knowing its phenology and removing the leaf biomass before leaf abscission, in order to allow simultaneous use of leaves to photosynthesis and food subtract to the larvae of P. ricini.