Etiology of root rot, yellows and wilt diseases of chickpea in Kermanshah province

Chickpea is a valuable and protein-rich pulse crop which is widely cultivated in more than 50 countries. Cultivation of chickpea in rotation with cereals can improve soil fertility through the process of symbiotic nitrogen fixation. Among the chickpea producing provinces in Iran, Kermanshah province has the first rank of chickpea production. Root rots and wilt have been considered the most devastating diseases limiting chickpea production in Kermanshah Province. However, the etiology of these diseases has not been thoroughly investigated. Therefore, the present study aimed to identify the fungal species causing wilt, yellowing and root rot in Kermanshah province, identify the dominant species and determine the prevalence of the disease in different regions of the province.

One hundred ninety-four chickpea fields, representative of the main planting areas throughout Kermanshah province, were surveyed during growing seasons 2011-2015. In each field, at least four diseased plant samples showing yellowing or wilting symptoms were collected, kept in paper bags, and transferred to the laboratory. 5 mm long pieces of root and stem of affected plants were prepared, surface sterilized and plated on Water Agar. The culture plates were incubated at a temperature of 25°C and examined on a daily basis. Pure cultures were obtained using either the hyphal-tip or single spore techniques. The isolates were then morphologically identified using available descriptions from the literature. Out of the abundant isolates, a total of 288 were selected for further investigation regarding their pathogenicity and aggressiveness. To prepare the inoculum, oat seeds were soaked in water for 24 hours and then transferred to 500 ml flasks. The flasks were autoclaved at a temperature of 121°C for 20 minutes, twice on two consecutive days. Each fungal isolate was cultured on five plates containing Potato Dextrose Agar (PDA) medium. Then, the autoclaved oat seeds were added to the plates. The plates were then incubated at 25°C for two weeks until the fungus completely covered the seeds surface. The pots (4 cm in diameter and 12 cm in height) were filled to a height of 6 cm with an autoclaved soil mixture (field soil / sand at a ratio of 2:1), then 2 ml of inoculum was applied to the soil surface, the inoculum was covered with one cm of autoclaved soil, the two seeds of chickpea cultivar, Bivanij were placed on the soil surface, Finally, the seeds were covered with 2 cm of soil. In this test, three replicates were considered for each isolate. The control pots were mock inoculated with uninfested oat seeds. The pots were kept in the growth chamber for a maximum of five to six weeks at 25-28 ° C. The disease severity was rated according to a 0-4 scale.

Based on morphological characteristics, eight fungal species including Fusarium oxysporoum, F. solani, F. equiseti, F. proliferatum, F. verticillioides, F. culmorum, Macrophomina phaseolina and Rhizoctonia solani were identified. Based on the results of pathogenicity test, except for F. verticillioides and F. culmorum other species were identified as pathogenic. Among these, F. oxysporum and F. solani species complex were classified as the most common and most aggressive pathogens. F. equiseti and F. proliferatum were ranked as weakly aggressive pathogens. In this study, vascular discoloration, a major characteristic of the pathogenic isolates of F. oxysporum, was observed in only a few inoculated plants suggesting that most of the recovered isolates did not belong to F. oxysporum f. sp. ciceri. Disease symptoms triggered by most of the isolates of F. oxysporum species complex in this study are consistent with those of F. redolens. However, accurate identification of these isolates requires a combination of molecular protocols and detailed morphological studies.

Our results showed that Fusarium species are the main agent causing root rot, yellowing and wilt on chickpea in kermanshah province. Among these, F. oxysporum species complex was the most common and most aggressive species. However, contrary to previous reports, most of the F. oxysporum isolates examined in this study did not belong to F. oxysporum f. sp. ciceri. Since the accurate pathogen identification is crucial for efficient disease management, accurate identification of the pathogen needs to be confirmed using molecular protocols. We also concluded that F. proliferatum is a weak pathogen of chickpea root. This is the first report of pathogenicity of F. proliferatum on chickpeas.