Ferrugem Asiática (Phakopsora pachyrhizi) da soja (Glycines max.) na cultura do feijão (Phaseolus vulgaris)

Abstract

This dissertation reports three researches carried out at Ponta Grossa State University. The elaboration and validation of a diagrammatic scale to assess Asian rust severity in common bean crops; the verification of commonly used cultivars in Paraná resistance levels to Asian rust disease; and the sowing date influence on Asian rust severity levels. To elaborate the diagrammatic scale, fifty leaflets from JALO PRECOCE and RADIANTE cultivars were collected. Based on the Quant program, the maximum severity levels were determined (77,10%) as well as the minimum levels (1,02%) and through the “Weber and Fechener’s stimulus law” six other intermediate severity levels were obtained (2,3%)-(5,11%)-(10,97%)-(21,99%)- (39,19%)-(59,58%). The real severity determination was done through the randomly collection of fifty leaflets with different severity levels. Scale validation was performed by ten raters only five of them were experienced in phytopathology. The leaflets assessment was firstly carried out without the scale and later with the use of it. As a result, they not only improved their precision, as well as presented absolute errors levels lower than 10% when supported by the scale, agreeing with Nutter’s data. Seven among the ten raters were accurate. Aiming at assessing cultivars resistance levels to Asian rust disease, under natural infection conditions, twenty-three common bean cultivars were submitted to assessment, PRETO, CARIOCA and MANTEIGÃO. Based on the results, it may be seen that the cultivars from MANTEIGÃO group (JALO PRECOCE and RADIANTE) presented a high severity level to the disease with severity levels of 40%, while CARIOCA and PRETO group cultivars demonstrated levels varying from resistant to susceptible. Among the cultivars, the lowest severity levels were found in the IPR-36 (2,6%), FTBONITO (3,7%) and IPR-CHOPIM (3,8%) cultivars. Concerning to the cultivars cycle, it could be observed that the earliest mature were the ones which presented the highest severity levels to Asian rust. In conclusion, it may be affirmed that the common bean resistance levels to Asian rust vary from resistant to susceptible. The MANTEIGÃO group cultivars presented the highest resistance levels to the disease. In order to assess two common bean cultivars response to Asian rust (IPR SARACURA e IPRUIRAPURU),sowed in ten different dates, an experiment was conducted. The first season was sowed on 04/10/2005 and the nine others followed a fifteen-day break until the last one sowed on 15/02/2006. Severity assessments were carried out in all phenological stages in each sowing date. The results show that only in the seventh season, when the common bean plants were in the R-8 phenological stage, the Asian rust presence could be confirmed. There were statistics differences among the sowing date, however no meaningful differences could be observed in the first nine seasons among the cultivars according to the severity percentage or to the AACPD. The IPR-SARACURA cultivar was, nevertheless, statistically higher to IPR-UIRAPURU in the tenth season. In conclusion, the later the sowing is done, the earlier the Asian rust is found in the beans crop. In addition, Asian rust negatively influenced on the cultivars bean yield potential, considering that the weight of 1000 bean was the only component to be affected.