Susceptibility of Maize Inbreds and Incidence of Symptomless Infection by the Head Smut Pathogen, Sphacelotheca reiliana

A real-time PCR assay was used to compare seedling infection by Sphacelotheca reiliana, the causal agent of head smut, among five inbred genotypes representing low, moderate, and high susceptibility to the disease. Seeds were coated with teliospores and planted in autoclaved field soil in a growth chamber. Incidence of seedling infection at growth stage V3 differed between an inbred genotype of low susceptibility and those of moderate and high susceptibility, but did not differ between the high and moderately susceptible groups (P < 0.05). The real-time PCR assay was also used to compare infection status at early and late vegetative stages with observable symptoms in the field. We detected infection via real-time PCR in maize at both growth stages during field trials conducted in Texas and California but observed no disease symptoms (smutted ears or tassels). Notably, the fungus was present in up to 31% of the ear shoots in plots without disease symptoms. The real-time assay can be a useful tool for screening seedling-stage host resistance, and for better understanding the progress of infection in different maize genotypes. The field data suggest that asymptomatic infection is much more common than previously thought, and may have important implications for the epidemiology of this fungus under diverse plant resistance and growing conditions. Accepted for publication 11 December 2015. Published 5 January 2016.

Real-Time PCR Assay for Detection of Sphacelotheca reiliana Infection in Maize (Zea mays) Seedlings and Evaluation of Seed Treatment Efficacy

Head smut of maize, caused by the fungus Sphacelotheca reiliana, is an economically important disease in all major maize-producing countries. Although seed treatments are commonly used for management purposes, evaluating these treatments for efficacy is both time consuming and inefficient. Therefore, in order to improve the capacity for evaluating seed treatment fungicides, we developed a real-time PCR-based seedling assay for S. reiliana infection. We optimized growth chamber conditions and inoculation methods to achieve infection incidence of 60 to 80% in inoculated, nontreated controls. The effects of five commercially available fungicidal seed treatment formulations on seedling infection incidence were compared by PCR analysis of root and mesocotyl tissues. Tebuconazole, fludioxonil, sedaxane, and Maxim Quattro (fludioxonil+mefenoxam+azoxystrobin+thiabendazole) reduced the incidence of infection (P < 0.05) compared with the control, but no difference was found between the azoxystrobin treatment and the control. All rates tested for both sedaxane and tebuconazole were equally effective for seeds coated with 106 teliospores∙seed–1. Sedaxane, at a rate of 0.1 mg/kernel, eliminated seedling infection if seeds were infested with a low inoculum concentration (101 teliospores∙seed–1). The assay developed here is a valuable tool not only for the detection of fungal infection at the seedling stage, but also for testing the relative efficacies of seed treatments for reducing incidence of infection.

Evaluation of Fungicides for the Control of Bakanae Disease of Rice Caused by Fusarium moniliforme (Sheldon)

Bakanae is one of the major diseases of rice in Bangladesh and causes substantial yield loss. To control the disease eleven fungicides from different fungicidal groups were evaluated for their efficacy against seed-borne fungus, F. moniliforme as seed treatment both in the laboratory and in the seed-bed during 2011 and 2012. In the laboratory the fungicides were evaluated at three concentration levels viz 2.5, 3.0 and 3.5 gm/L/kg seeds. Overall performance of the fungicides was found to be better in suppressing the seed-borne F. monilifome and increasing seed germination. Among the fungicides, Bavistin, Sunphanate, Nativo and Carzeb completely inhibiting the growth of F. moniliformeinvitro condition at their low (2.5 gm/L) concentration. Efficacy of the fungicides reduced to some extent when the treated seeds were washed with fresh water except Bavistin. Maximum (85%) average germination was found in Bavistin and Greenzeb treated seeds. The promising fungicides further evaluated to control seedling infection at low (2.5 gm/L) concentration and resulted significant reduction of bakanae infected seedlings in pot soil and in seed bed.Bangladesh Rice j. 2015, 19(1): 49-55

Przenoszenie się grzyba Ustilago perennans Bostr. z nasionami rajgrasu wyniosłego [Transmission of Ustilago perennans Rostr. with tall oat grass seeds]

It was established that the mycelium of <i>Ustilago perennans</i> does not grow into the pericarp and seed coat of <i>Arrhenatherum elatius</i> caryopses. The main source of seedling infection at this year .seeds sowing were mycelium and gemmes present in hull tissues whereas ait last-year seeds sowing-the spores wintering on the hull and caryopsis surfaces, as they proved to be more survived. The ability of the fungus to seedling infection was decreasing gradually with the seed ageing.