Amauri Bogo

Danos causados pela infecção de Gibberella zeae em trigo

Damages caused by infection of Gibberella zeae in wheat Fusarium head blight or wheat scab, caused by Gibberella zeae, is a disease of the floral infection, with frequent occurrence in regions where long periods of rain (> 48 h) and average temperatures (> 20 o C) occur after the wheat (Triticum aestivum) begins to flower. The reduction of grain yield, caused by nature infection of wheat scab in the field, has been quantified in different wheat cultivars during the harvests of 2001 and 2002, in the city of Passo Fundo, RS. All the wheat scab spikes, from the grain milk stage through maturation, had been identified and marked in an area of the 1 m 2 , being sampled three repetitions for wheat area. The scab and healthy spikes were harvested, dried, counted and threshed separately. The damages caused by wheat scab were calculated by the difference between the actual yield and the estimated yield potential based on the total numbers of spikes, the number of healthy spikes and the number of scab spikes. The average damage caused by wheat scab in 25 samples of wheat collected in 2001, was 13,4%, varying from 6,4 to 23,1%. In the 2002 harvest, the average damage in 18 samples, was 11,6%, varying from 3,1 to 20,5%. The average reduction in the grain yield for harvests of 2001 and 2002 were 394,4 Kg.ha -1 and 356,8 Kg.ha 1 , respectively. In the two harvests, the average damage caused by wheat scab, in the different cultivars, was 375,3 kg.ha -1 or 6,26 bags of wheat/ha.

Incidência e severidade de doenças de quatro híbridos de milho cultivados com diferentes densidades de plantas

Modern maize hybrids have greater yield potential than cultivars used in the past, particularly under stressful conditions such as high plant population and water deficit. It is possible that the yield advantage presented by modern genotypes is partially due to their better ability to resist major maize diseases. This experiment was carried out to evaluate the incidence and severity of maize leaf, stem, and ear diseases on hybrids usually grown in Southern Brazil, under different plant populations. A split plot design was used, with the main plots disposed in randomized complete blocks. Three plant populations, equivalent to 50,000, 75,000 and 100,000pl ha-1, were tested in the main plot. The hybrids Ag 12, Ag 28, Ag 303 and Ag 9012, which were cultivated expressively in the 60s, 70s, 80s and 90s, respectively, were tested in the split plot. The enhancement in plant population promoted increases on the incidence of stem diseases caused by Fusarium moniliforme, Colletotrichum graminicola e Diplodia maydis, especially on Ag 12 and Ag 28, contributing to decrease their stem standability at harvesting. The hybrid Ag 9012 had lower incidence and severity of ear diseases caused by Fusarium moniliforme e Diplodia maydis, regardless of plant population. The hybrid Ag 9012 did not express lower severity levels of leaf diseases in relation to the older hybirds used in the trial.

Diversidade genética em acessos de feijão (Phaseolus vulgaris L.)

The correct characterization of genetic resources allows to identify sources of variability, a genetic profit during the plant breeding and use of these resources in the crop science. This research was aimed at evaluating genetic divergence in bean accessions of a germplasm of Santa Catarina, through interrelation among the agronomic character descriptor. Twenty bean (Phaseolus vulgaris L.) accessions were evaluated carried out in October 2005, using the randomized block design with three replications. The genotypes were studied using multivariable techniques to measure genetic divergence represented by the generalized distance of Mahalanobis. On the basis of the genetic similarity matrix, it was generated average distance grouping. Among 12 variable evaluated, the weight of 100 seeds had the higher contribution in the separation of the genotypes, followed for the pod width, pod length and yield of grains. The BAF 42, BAF 46, BAF 47 and BAF 57 accessions had the high productivity level and it must be better characterized to be incorporated in the programs of genetic breeding or use of these resources in the crop science.

Modelo de ponto crítico para estimar danos de doenças foliares do trigo em patossistema múltiplo

A critical-point model to estimate damage caused by wheat leaf diseases in a multiple pathosystem Wheat leaf diseases cause damage by reducing photosynthetic activity in leaves. The objective was to obtain damage model equations for a wheat multiple pathosystem, by examining the relation between grain yield and the incidence of leaf diseases at different plant growth stages. The experiments were carried in Lages and Sao Jose do Cerrito, SC, during the 2005/06 and 2006/07 crop seasons with cultivars Onix and BRS Louro. The gradient of disease incidence was obtained by the number of fungicide applications (one, two, and three) and three different fungicide rates: azoxystrobin+cyproconazol (40+16, 60+24 and 80+32 g of a.i. ha -1

Época de aplicação e desempenho de fungicidas no controle da giberela em trigo

The chemical control of the wheat scab can be affected by time of application and fungicide. In the 2004 growing season, the fungicides were applied in the plant growth stage of beginning of flowering, half of complete flowering and beginning of soft dough stage. In the 2005 growing season, one only fungicides application was done in the beginning of the flowering with a larger number of fungicides. The applications were done with manual spray, with CO2 gas pressure in an outflow of 200L ha-1. The intensity of wheat scab was quantified by the incidence, severity and index of giberela. Grain yield, weight of a thousand grains and the incidence of Fusarium graminearum in the grains were also evaluated. The high porcentual of wheat scab control occurred when the application was done in the beginning of the flowering. The fungicides metconazol (0.09L i.a. ha-1), tebuconazol (0.15), trifloxystrobin+tebuconazol (0.075+0.15), azoxystrobin+ciproconazol (0.060+0.024) and pyraclostrobin+epoxiconazol (0.099+0.037) reduced significantly the intensity of giberela wheat, obtaining average control of 46% on incidence, 46.6% on severity and 71.2% on index of giberela wheat. These fungicides showed grain yield average of 23.4%, but a low efficiency on F. graminearum infection control in grains.

Caracterização morfológica de isolados de Cryptosporiopsis perennans em diferentes meios de cultura

The mycelial growth and conidial production of nine isolates of Cryptosporiopsis perennans were evaluated on the culture media of potato-dextrose-agar acidified (PDA-acid), malt extract agar (MEA) and V8-agar (V8) under 12 hours of photoperiod at 21°C. Five mm-diameter disks taken from colonies grown for 14 days on PDA medium under 12 hours of photoperiod at 21°C were transferred to Petri dishes with 20 mL of each medium. Colonial morphology, mycelial growth, sporulation and spore dimension were evaluated after 13 days of incubation. The effect of the culture media varied according to isolates. Mycelial growth and conidial production were observed in all tested media. The culture medium V8 was the best medium tested for mycelial growth and conidial production, followed by MEA for all C. perennans isolates. In all culture media the isolates presented a fusiform conidial shape.

Rediscovery of Claviceps sorghi (Ascomycotina: Clavicipitaceae) in India

During last twenty years, endemic Claviceps sorghi was largely replaced in India by an introduced species Claviceps africana. Recently, C. sorghi was foundand isolated from Sorghum bicolor (Gulbarga, Karnataka). Macroconidia were smaller than in the type description, 7.6-14.5 (avg. 11.4) × 3.8–6.1 (avg. 4.8)μm; microconidia were rounded to oval, 2.5–3 μm in diameter. When plated, only the macroconidia underwent secondary conidiation. Sporulation was maintained only in cultures grown on sucrose-asparagine medium T2. Mycelium was reduced to sparse hyphae with numerous short conidiophores soon obscured by yeastlike conidial mass. RAPD patterns of isolates GUL, MH74 (Maharashtra), NAP7 and NAP5 (Andhra Pradesh)with 6 primers were almost identical and distinct from those of C. africana. Sequence of rDNA containing ITS1-5.8S-ITS2 region for isolate GUL (AJ306621) corresponded to that of the authentic material of C. sorghi (AJ242869) confirming thus the presence ofC. sorghi in Central India.

Biological multiple indexing and RT-PCR detection of latent viruses in apple plants

This study aimed to evaluate the suitability of a multiple biological indexing method of latent apple viruses. The method consisted of grafting five indicator species and two buds of the plant to be indexed on to one rootstock. Results showed that the sensitivity and efficacy of the MBI is adequate for reliable detection of Apple stem grooving virus, (ASGV), Apple stem pitting virus (ASPV) and Apple chlorotic leaf spot virus (ACLSV) of mother plant stock in certification programs. Sample analysis by RT-PCR confirmed the results of the diagnosis of ASPV and ASGV by multiple biological indexing. However, it did not detect ACLSV diagnosed by LL-S5 in three out of nine analyzed accessions. The coat protein gene of one of the accessions studied was cloned and sequenced. The annealing sites of primers used in unsuccessful amplification attempts were compared with data of the Genbank to explain the non-amplification of certain ACLSV isolates.

Incidência de podridões do colmo, grãos ardidos e rendimento de grãos em híbridos de milho submetidos ao aumento na densidade de plantas

The combination between plant density and hybrid choice is an important factor to enhance maize grain yield. The objective of this work was to evaluate the increasing of plant density on the incidence of stalk rot, rot grains and grain yield of two maize hybrids with contrasting tolerance to crowding. The experiment was carried out in Lages-SC, during the crop seasons of 2002/03 and 2003/04, in an area of no-tillage and monoculture, having a mixture of black oat and vetch as the preceding winter crop. The experimental design was a randomized block with split plot arrangement and three replications per treatment. Two hybrids were evaluated in the main plots: Speed (a single-cross hybrid tolerant to crowding) and AG 303 (a double-cross hybrid intolerant to crowding). Each hybrid was submitted to five plant densities in the split-plots: 25, 50, 75, 100 and 125 thousand plants per ha. The increase in plant density enhanced linearly the occurrence of stalk rot and rot grains for both hybrids and crop seasons. The fungus Colletotrichum graminicola was detected with great frequency in the stalk rot, regardless of hybrid and crop season, followed by Fusarium graminearum, F. verticillioides and Stenocarpella sp. The predominant fungi in rot grains were F. verticillioides, F. graminearum and Penicillium spp. The grain yield of AG 303 was less responsive to the increment in plant density. No association between the higher grain yield of the single-cross hybrid Speed at dense stands and the lower incidence of stalk rot and rot grains was detected.

Incidência de podridões do colmo, grãos ardidos e produtividade de grãos de genótipos de milho em diferentes sistemas de manejo

Maize monoculture is an usual practice in some regions of Brazil, being responsible for the growing damage caused by diseases. The objective of this work was to evaluate the effect of different maize production systems, contrasting in management investments, on the incidence of stalk rot, rot grains and grain yield. Four production systems were tested: S1 (low management level), S2 (medium), S3 (high) e S4 (designed to maximize the grain yield). The production systems differed in relation to plant density, row spacing, amount of fertilizer and irrigation use. Three genotypes were used for each production system: BRS Planalto (open-pollinated variety), Traktor (double-cross hybrid) and P32R21 (single-cross hybrid). The experiments were carried out during 2002/03 and 2003/04 grown seasons, in no-till system and a monoculture area, having a mixture of black oat and vetch as the preceding winter crop. The experiments was a split-plot arranged in randomized complete blocks design with four replications. In both grown seasons, regardless management system, open-pollinated variety BRS Planalto showed higher stalk rot than the hybrids. Colletotrichum graminicola was the main pathogen associated with stalk rot. Grain yield ranged from 3,986 to 13.489kg ha-1 in 2003 and from 1,787 to 13.849kg ha-1 in 2004, depending on genotype and crop management system. The highest values of grain yield were obtained in S4 with the single-cross hybrid. The incidence of rot grain was low (below 6%) during the whole experimental period. Fusarium verticillioides was the main pathogen associated with rot grain. There was no association between incidence and causal agent of stalk rot and rot grain. It was not possible to identify a crop management system that was more efficient to reduce incidence of stalk rot and rot grain.