-The high degree of variability of the fungus

Os objetivos deste trabalho foram avaliar o nível de resistência de oito híbridos comerciais de milho aos patógenos Puccinia polysora Underw e Physopella zeae (Mains) Cummins e Ramachar, e comparar a eficiência dos métodos da área abaixo da curva de progresso da doença (AACPD) e dos parâmetros de estabilidade fenotípica, na avaliação dessa resistência. Em quatro ambientes nas regiões Sudeste e Centro-Oeste do Brasil foram realizadas cinco avaliações da severidade das doenças, em intervalos de dez dias a partir dos 60 dias após a semeadura, utilizando uma escala diagramática com notas. Os parâmetros de estabilidade fenotípica estudados foram o coeficiente de regressão linear (b) entre a época de avaliação (x) e a severidade da doença (y) e o coeficiente de determinação (R²). No caso de P. polysora, ambos os métodos utilizados mostraram-se eficientes na discriminação do nível de resistência dos híbridos, permitindo a classificação de modo semelhante. Quanto a P. zeae, não houve boa concordância entre os dois métodos, especialmente porque a discriminação do nível de resistência entre híbridos não foi expressiva. Os híbridos mais resistentes a P. polysora foram Z 8392, C 909 e C 333, e os mais suscetíveis, P 3069, AG 9012 e C 956. Os destaques, em termos de resistência a P. zeae, foram C 909 e C 333, e os híbridos mais suscetíveis, P 3069 e AG 9012.

In agricultural areas of Brazil, where there is no establishment of cover crops in the off-season and in fruit orchards, an increase in Chloris elata infestations, syn. Chloris polydactyla, has been observed. With the purpose to evaluate the response of three populations (Itaberaí - GO, Matão - SP e Jaboticabal - SP) of C. elata to herbicides sprayed before and after emergence, four experiments were conducted. In the first one, the differential tolerance of three C. elata populations to the herbicide glyphosate (0, 0.18, 0.36, 0.72, 0.96, 1.44, 2.88, 5.76 and 11.52 kg a.e. ha-1) was studied. In the other experiments, the control of the three populations by herbicides applied in pre-emergence (clomazone, diclosulam, flumioxazin, isoxaflutole, chlorimuron-ethyl, metribuzin, S-metolachlor, sulfentrazone and trifluralin) or in post-emergence (clethodim, fenoxaprop-p-ethyl, fluazifop-p-butyl, haloxyfop-methyl, quizalofop-p-tefuryl, mesotrione, nicosulfuron, tembotrione, glufosinate-ammonium, paraquat and glyphosate) was evaluated. The population from Jaboticabal was more susceptible to glyphosate than Itaberaí and Matão, at smaller doses. In pre-emergence, clomazone, isoxaflutole, metribuzin, S-metolachlor and trifluralin were effective in controlling the three populations. The same results were observed for clethodim, fenoxaprop, fluazifop, haloxyfop, quizalofop, paraquat and glyphosate, when sprayed on plants with 2-6 tillers. C. elata populations differed for the herbicides flumioxazin, chlorimuron-ethyl and nicosulfutron.

In Brazil, in agricultural areas where there is no establishment of cover crops in the off season, as well as in citrus orchards in the state of São Paulo, an increase in the infestation of Chloris elata has been observed. This is a perennial species, propagated by seeds and short rhizomes, erect and slightly caespitose. With the objective of evaluating the growth and development of plants from two accessions of C. elata, a greenhouse experiment was conducted. The experimental design was completely randomized, in a 2 (accessions of C. elata) x 15 (evaluation periods) factorial arrangement, with four replications. Fifteen destructive evaluations were performed 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, 84, 91, 98, 112 and 126 days after sowing (DAS) both accessions of C. elata (Itaberaí from Goiás and Matão from São Paulo State). At each evaluation, four plants (replications) were randomly sampled and the height of the main culm, the number of tillers and inflorescences (flower+seed) per plant, the leaf area and dry matter of leaves, culms, roots, inflorescences and total (leaves+culms+roots+ inflorescences) were analyzed. The two accessions showed a slow initial development and growth (up to 63 DAS), mainly in root growth; however, the development of new tillers increased rapidly in the initial phase. During the first 63 DAS, the percentage distribution of dry matter was higher in the foliage, followed by culms and roots. In the final evaluation, the relation was culms followed by leaves, roots and inflorescences. Plants of Matão formed denser clumps, with culms of greater mass, while those from the Itaberaí showed higher height and greater foliage.