Cultural practices and genetic resistance as factors affecting soybean stem canker and plant yield in the Cerrado

Abstract

Field experiments were conducted in the 1995-96 soybean (Glycine max) growing season to evaluate the effects of cultural practices and host genetic resistance on the intensity of soybean stem canker, caused by Diaporthe phaseolorum f.sp. meridionalis (Dpm). Experiments were conducted in a commercial field severely infected in the previous (1994-95) season. In one study, minimum tillage (MT) and no-tillage (NT) cropping systems were investigated for their effects on disease development and on plant yields in cvs. FT-Cristalina (susceptible) and FT-Seriema (moderately resistant). Another study evaluated the effects of plant densities (8, 15, 21 and 36 plants/m) on disease development in cvs. FT-Cristalina, FT-101 (moderately resistant) and FT-104 (resistant). Disease incidence and severity were consistently lower in NT than in MT, and plant yields were increased by 23% and 14% in the NT system for the susceptible and moderately resistant cultivars, respectively, compared to the yields in the MT system. The Gompertz and Logistic models described well the disease progress curves in all situations. For both susceptible and moderately resistant cultivars, disease severity increased proportionately to the increase in plant densities. At the end of the season, 100% of the plants of cv. FT-Cristalina were infected by Dpm, at all plant densities. Disease levels on cv. FT-101 were intermediate while only very low disease levels were recorded on cv. FT-104. There was a consistent negative correlation between stem canker severity and yield. Some practices demonstrated potential for direct application in disease control, and could be combined considering their additive effects.

Survival of Diaporthe phaseolorum var. caulivora (causal agent of soybean stem canker) artificially inoculated in different crop residues

“…In Brazil from 1993 to 1996 SSC was considered one of the main limiting factors in soybean production in the Cerrado, when the farmers adopted NT cropping practices (Freitas et al, 2002). The use of Dpm resistant soybean cultivars led to an effective control of this disease.…”

“…Most inoculum for the disease development is thought to be ascospores from perithecia or conidia from picnidia developing on overwintered infested crop residue, which are dispersed by splashing raindrops and windborne rain (Backman et al, 1985;Freitas et al, 1998). Regarding the presumed reduction of inoculum by cropping practices, and the putative enhancement of perithecial formation in NT, it must be acknowledged that field evidence is very controversial: while some studies have detected more stem canker in NT (Rothrock et al, 1985;Tyler et al, 1987), others, like Freitas et al (2002) in Brazil found significantly less SSC in NT fields. Residues derived from NT provide soil cover and are a potential survival and Survival of Diaporthe phaseolorum var.…”

Soybean Stem Canker Caused by Diaporthe caulivora; Pathogen Diversity, Colonization Process, and Plant Defense Activation

“…The scale includes severity values (Ni) that ranged from 1 to 7 ranked as follow: (1) plants without external symptoms; (2) stem lesions equal to or less than 15 mm; (3) stem lesions equal to or less than 25 mm; (4) stem lesions up to 50 mm in length, sometimes showing foliar symptoms; (5) stem lesions up to 75 mm long, stem girdling, typical interveinal foliar chlorosis; (6) stem lesions larger than 75 mm, plant showing interveinal foliar necrosis; and (7) dead plants (Supplementary Figure 2). Disease severity index was calculated using the formula: S = S(ni/nt × Ni), where S = severity index; ni = number of individual plants rated for severity value Ni; and nt = total number of plants per treatment (Freitas et al, 2002). The area under disease progress curve (AUDPC) was calculated according to Shaner and Finney (1977) at 14 dpi, using the formula:…”

Fusarium wilt incidence and common bean yield according to the preceding crop and the soil tillage system

“…No-till (NT) practices are presently widely adopted for several grain crops in Brazil (Freitas et al, 2002) and, although bean yields are usually higher than the average national mean in the NT system, Paula Junior et al (2004) claimed that, after an increase in the initial years of NT adoption, yields gradually decrease, partially due to the increase in the severity of soilborne diseases. One of the problems associated with the NT system is soil compaction, which may aggravate Fusarium diseases (Miller & Burke, 1985).…”

“…Bean growers have been adopting the NT cropping system since the early 1990s, also because it reduces production costs substantially. Nevertheless, no research on the effects of this practice on common bean Fusarium wilt has been published, even though recent results with beans and soybeans have shown reduction of some soil fungi in the NT, as compared to the conventional cropping (CC) system (Freitas et al, 2002;Napoleão et al, 2005).…”