Manoel Delintro de Castro Neto

Effect of nitrogen doses on disease severity and watermelon yield

Nitrogen fertilization is an important step for watermelon (Citrullus lanatus) production due to its influence over yield, fruit quality, and disease severity. Currently, the gummy stem blight (Didymella bryoniae) and the downy mildew (Pseudoperonospora cubensis) can be taken as the most important watermelon diseases, since they impose severe impairment to the crop. Furthermore, studies focusing on plant responses to nitrogen fertilization regarding fruit yield and quality, and disease resistance are rare. Hence, the present study aimed at evaluating the effect of nitrogen doses on fruit yield and quality, and on disease prevalence in watermelon. Two experiments were carried out at the Universidade Federal de Tocantins, employing sprinkler irrigation, in an area previously used to grow watermelon. The experimental design was blocks at random, with five treatments (N doses, applied twice as side-dressing, in kg ha-1, as follows: T1= control treatment without N, T2= 20, T3= 40, T4= 80, and T5= 120), and four replications. Urea (45% N) was used as the N source. In the first assay, the highest fruit yield and average weight were observed when 40 kg ha-1 of N were applied. The highest severity of the gummy stem blight was observed when the highest nitrogen doses were applied (80 and 120 kg ha-1). In the second assay, the highest severity levels of the gummy stem blight, as well as of mildew, were observed again when N doses were the highest (80 and 120 kg ha-1). The lowest severity levels for both diseases were observed in the control treatment.

Identification of physiological races of Magnaporthe grisea in areas of rice irrigated in the State of Tocantins

Identification of physiological races of Magnaporthe grisea in areas of rice irrigated in the State of Tocantins In Brazil, the most important disease in rice is blast, which is caused by the fungus Magnaporthe grisea. This disease is considered to be a limiting factor for rice productivity. This work aimed to determine the prevalent races of the rice blast pathogen M. grisea in the state of Tocantins, in order to study the variability in the region and make it possible to develop and recommend blast-resistant rice cultivars. To assess this information, infected leaves were collected from three experimental sites, each consisting of multilines and a varietal mixture of irrigated rice in Tocantins state. A total of 250 monosporic isolates were obtained. Subsequently, these isolates were inoculated in the International Standard Differential (ISD). A total of 45 races were identified, where the most prevalent race was IA1 (24.8% of the isolates), followed by IA-65 (11.2%) and IA-33 (6.4%), respectively. The highest number of races was found in the experimental site located at Lagoa da Confusao, followed by Formoso do Araguaia (Projeto Formoso) and Unitins-Agro, respectively. In the population of M. grisea under study, a high variability was found with prevalence of the race groups: IA, IB and ID.

Reaction of melon genotypes to the gummy stem blight and the downy mildew

The gummy stem blight (Didymella bryoniae) and the downy mildew (Pseudoperonospora cubensis) are two foremost melon (Cucumis melo) diseases, considering their effects on yield and fruit quality. Despite the importance of such diseases, relatively few studies have been done so far on the identification of resistance sources to D. bryoniae and P. cubensis in Brazil. This work aimed at evaluating the resistance of commercial melon genotypes to the gummy stem blight and the downy mildew. Firstly, the most aggressive and representative D. bryoniae isolate was selected. Subsequently, the resistance of 86 melon genotypes to stem infection was studied upon greenhouse conditions by inoculating with the previously selected isolate. Afterwards, the resistance to mildew and leaf infection by D. bryoniae of 28 melon genotypes was evaluated in the field, under natural infection. In the greenhouse, all 86 melon genotypes were infected and showed stem infection symptoms caused by D. bryoniae four days after inoculation. Nevertheless, a significant variation on the resistance levels of the melon genotypes was found. Under field conditions and natural inoculation, genotypes Taslaki and Sary Juliabi were the most susceptible to leaf infection by D. bryoniae, significantly differing from the other genotypes. The lowest levels of susceptibility were identified in genotypes Perlita Busle S1, Valenciano Eliptico, Glaver, MR1, and 2526. All genotypes were susceptible to the downy mildew, albeit differing in susceptibility levels.

Eficiência no uso de fósforo de variedades de arroz cultivadas em solos de várzea irrigada

Efficiency in the use of phosphorus by rice varieties grown in lowland soils Rice stands out as one of the most important crops in the world, because of its easy adaptability to distinct edaphoclimatic conditions. Rice is cultivated and consumed worldwide and stands out by the large production and cultivation area, playing strategic economic and social roles. In Brasil, the largest rice productions are obtained in lowland ecosystems. This work aimed to study the efficiency in phosphorus use by rice varieties in lowland areas in the southwest of Tocantins State. The treatments involved eight rice commercial varieties (BRS-Jacana, Best2000, BRS-Guara, BRS-Alvorada, BRA-01381, AN-Cambara, BRS 7-TAIM and EPAGRI-109), which were farmed in two distinct environments. In order to simulate environments with low and high phosphorus levels, P 2 O 5 was used at the levels of 20 and 120 kg ha -1 respectively. The experiments were carried out in a randomized complete blocks design, with four replications. Grain yield was used to classify the varieties regarding the efficiency in use and response to phosphorus application. Was shown that only the variety BRS-Alvorada was efficient in using phosphorus and responsive to its application.

Danos causados por doenças fúngicas no arroz cultivado em várzeas no Sul do Estado do Tocantins

This study aimed to evaluate the damages caused by the fungal diseases in rice production under conditions of lowland at the State of Tocantins. The experimental design was a randomized blocks with four replications, in a factorial scheme of 26 (genotypes of irrigated rice) x 2 (plots treated or untreated with fungicides). The fungicide treatment consisted of three applications, the first one was done 35 days after planting with thiophanate methyl (0.5 L ha-1), the second application was done in the booting stage of rice with trifloxystrobin + propiconazole (0.6 L ha -1) and the third application was done with 5% of panicles issued with trifloxystrobin + propiconazole (0.6 L ha-1) + tebuconazole (0.75 L ha-1). The following evaluations were performed: leaf and panicle blast severity, brown-spot severity, grains spots, 100 seed mass, and productivity. The fungicide treatments decreased around 69% the blast severity on leaves and 54% on panicles of most genotypes. There was not any statistical difference in the treatment with or without fungicide for brown-spot, however there was statistical difference among the genotypes. In plants treated with fungicides there was an increase of 0.52 g (17.6%) in the mass of 100 seeds and 1000 kg ha-1 in the productivity (12.6%). The maximum values obtained in 100 seeds mass and yield were 3.19 g and 9270 kg ha-1, respectively.

Diversidade de Magnaporthe grisea em arroz de terras altas no sul do Estado do Tocantins, na safra 2008/09

The rice blast, caused by the fungus Magnaporthe grisea, is one of the most important rice diseases in Brazil and in the world, mainly in upland conditions. This work aimed to identify the physiological races of M. grisea in commercial fields of rice cultivated in the upland system in Southern Tocantins State. Samples of rice plants containing blast symptoms were collected in the experimental field of the Federal University of Tocantins, Campus of Gurupi and commercial fields in the following municipalities: Alianca, Duere, Figueiropolis and Peixe. For the identification of M. grisea races, monosporic isolates were prepared in the laboratory and differential lineages were planted in a greenhouse. A total of 21 physiological races of M. grisea distributed in six groups of races from the International Standard Differential (ISD), where the most prevalent groups were IA and ID, comprising 52.38% and 14.28% of all isolates, respectively. The four most prevalent races were IA-1, IA-33, IC-1 and ID-9, of which IA-1 is considered the most aggressive. The highest number of races was found in the cultivar Primavera.

Seleção de genótipos de arroz para integrar uma mistura varietal visando o controle da brusone

A brusone, causada por Magnaporthe oryzae (Herbert) Barr é uma das doenças mais importantes na cultura do arroz. Várias estratégias de manejo da doença, como o uso de genótipos resistentes têm sido utilizadas, entretanto, o grande número de raças do patógeno dificulta a obtenção de cultivares com resistência durável. Neste contexto, o uso da mistura varietal pode constituir uma estratégia viável e promissora no controle da doença. Assim, objetivou-se com este estudo avaliar a reação de cultivares de arroz às raças de M. oryzae e a eficiência da mistura varietal na redução da severidade da brusone em condições Santos, G.R.; Chagas, J.F.R.; Castro Neto, M.D.; Fidelis, R.; Leão, E.U. Seleção de genótipos de arroz para integrar uma mistura varietal visando o controle da brusone. Summa Phytopathologica, v.43, n.4, p.290-296, 2017.