Rust (Uromyces viciae-fabae Pers. de-Bary) of Pea (Pisum sativum L.): Present Status and Future Resistance Breeding Opportunities.

Uromyces viciae-fabae Pers. de-Bary is an important fungal pathogen causing rust in peas (Pisum sativum L.). It is reported in mild to severe forms from different parts of the world where the pea is grown. Host specificity has been indicated in this pathogen in the field but has not yet been established under controlled conditions. The uredinial states of U. viciae-fabae are infective under temperate and tropical conditions. Aeciospores are infective in the Indian subcontinent. The genetics of rust resistance was reported qualitatively. However, non-hypersensitive resistance responses and more recent studies emphasized the quantitative nature of pea rust resistance. Partial resistance/slow rusting had been described as a durable resistance in peas. Such resistance is of the pre-haustorial type and expressed as longer incubation and latent period, poor infection efficiency, a smaller number of aecial cups/pustules, and lower units of AUDPC (Area Under Disease Progress Curve). Screening techniques dealing with slow rusting should consider growth stages and environment, as both have a significant influence on the disease scores. Our knowledge about the genetics of rust resistance is increasing, and now molecular markers linked with gene/QTLs (Quantitative Trait Loci) of rust resistance have been identified in peas. The mapping efforts conducted in peas came out with some potent markers associated with rust resistance, but they must be validated under multi-location trails before use in the marker-assisted selection of rust resistance in pea breeding programs.

Controle comparativo da ferrugem asiática da soja com fungicida triazol ou mistura de triazol + estrobilurina / Comparative control of soybean rust by a triazol fungicide or a mix of triazol + strobylurin

Fungicidas triazóis e suas misturas com estrobilurinas são os mais utilizados no controle da ferrugem asiática em soja. Mudanças na sensibilidade do fungo aos fungicidas requerem estudos continuados sobre a eficácia destes compostos. Neste trabalho, um estudo comparativo foi realizado, onde um triazol (tebuconazole) e uma mistura de triazol + estrobilurina (epoxiconazole + piraclostrobina) foram avaliados quanto ao controle da ferrugem da soja, com aplicações em épocas (V9, R4 ou R5.3) e número (1, 2 ou 3) variáveis. Utilizaram-se 64 parcelas de campo da cultivar Nidera 5909 AG, distribuídas em blocos casualizados. A intensidade da ferrugem foi medida em cada terço da planta, através de sete contagens de lesões e urédias, posteriormente convertidas a severidade (%). Esta foi superior a 40% nas plantas onde não foi aplicado fungicida. O progresso da ferrugem foi maior no terço inferior das plantas. As aplicações realizadas a partir do estádio V9 (haste com nove folhas) resultaram em melhor controle. A mistura de triazol + estrobilurina foi mais efetiva que o triazol. O progresso da doença ocorreu mais pelo aumento das lesões, pois o número de urédias por lesão pouco variou entre tratamentos.

Triazol and their mixtures with strobylurins are the main fungicides used to control Asian rust on soybeans. Shifting in fungal sensibility to fungicides demands continuous monitoring on the efficacy of such compounds. In this research a comparative study on rust control was carried out with the fungicide tebuconazol (triazol) and the mixture of epoxiconazol + pyraclostrobin (triazol + strobylurin), which were sprayed once, twice or three times from different plant growth stages (V9, R4, or R5.3). A total of 64 randomized plots of Nidera 5909 AG soybeans were assessed for number of lesions and uredia, later converted into percent severity for each third part of the plant (lower, medium, and upper). Rust severity was over 40% on non-treated plants. Disease progress was higher at the lower third. Spray applications began at V9 (main stem with nine trifolia) resulted in better rust control. The mix of triazol + strobylurin was more efficacious than the triazol alone. Disease increase was mainly driven by the amount of lesions, since the number of uredia per lesion did not vary significantly among treatments.