Chlamydospore concentration for assessment of Fusarium root rot on common bean

Abstract

Fusarium root rot caused by Fusarium solani f. sp. phaseoli (Fsp) is widely distributed in Latin America. Experiments involving artificial inoculations could be better compared whether the number of Fsp infective propagules is well quantified by using chlamydospores. This study aimed to define the adequate concentration of chlamydospores of Fsp for assessment of the disease severity under controlled conditions. In greenhouse, two experiments were performed, where common bean susceptible genotypes were sown in a substrate infested with 0, 1000, 2000, 3000, 4000, 5000 or 6000 chlamydospores g -1 of substrate. Plants were rated for disease severity at 30 d after emergence. Linear response plateau was used to represent the relationship between disease severity and concentration of chlamydospores in the substrate. According to our results, concentrations between 4500 and 5000 chlamydospores g -1 of substrate maximizes the disease severity and can be recommended to evaluate large-scale screenings of bean germplasm.

Linking physiological parameters with visible/near-infrared leaf reflectance in the incubation period of vascular wilt disease

“…Specifically, it has been shown that the increase of inoculum of F. oxysporum showed an increase on the incidence, mortality (20%), the severity of the disease and number of lesions on gladiolus roots (Riaz et al, 2008). Additionally, it was found a high coefficient of determination (R 2 = 0.94) on the linear relationship between the severity of the disease generated by F. solani in bean plants and the concentration of chlamydospores in the substrate (Nicoli et al, 2013).…”

Potential worldwide distribution of Fusarium dry root rot in common beans based on the optimal environment for disease occurrence

“…oxysporum f.sp. gossypii and phaseoli , and incidences of wilt in cotton [ 63 ], root rot on peanuts [ 64 ], root rot on barley [ 65 ], and wilt incidence in cotton [ 66 ] and the common bean [ 17 ] respectively are all density-dependently modulated, thus suggesting a general pattern. The intermediary aggressiveness of pathogens may be a result of evolutionary mechanisms that regulate density-dependent populations to maintain their fitness in the long term [ 59 ].…”

“…Three inoculum densities were selected according to published data regarding the disease severity/inoculum density relationship. The inoculum densities adopted were the following: 1200 CFU/g of soil based on field experiments and controlled environment tests with the common bean and FSSC [ 23 ]; 3700 CFU/g of soil in greenhouse experiments with the same pathosystem as above [ 24 ]; and 4500 CFU/g of soil based on greenhouse tests to estimate the dry root rot severity according to increasing concentrations of FSSC chlamydospores [ 17 ]. The inoculum density that most correlated with dry root rot records was then considered a spatial proxy for the disease.…”

“…In this study, we used the inoculum threshold approach represented by inoculum density, a highly used measure for epidemiological studies [ 17 ], easily estimated in field-soil samples. Although widely distributed in tropical regions of South America and Africa [ 18 ], no consensus has been reached on the lower inoculum threshold associated with dry root rot occurrence in common beans.…”

Virulent Fusarium isolates with diverse morphologies show similar invasion and colonization strategies in alfalfa

“…During the infection process, the macroconidia and microconidia of Fusarium can attach to the surface of plant rhizomes and spread to other plants as secondary inocula and infectious agents (Rekah et al, 2000;Ohara and Tsuge, 2004). Chlamydospores are more durable survival structures in soil, more adaptable to adversity than macroconidia and microconidia, therefore are more contagious (Nicoli et al, 2013;Akhter et al, 2016). Taken together, conidia play a crucial role in the occurrence and circulation of root rot, and the quantity and growth rate of conidia also affect Fusarium infection and colonization.…”