Effect of seed-borne fungi on seed health of native populations of Iranian cumin (Cuminum cyminum L.)

Abstract

Seed borne diseases caused by fungal pathogens are one of the most important threats that reduce the quantity and quality of cumin production every year all over the world. Hence, the first step in this research was to identify the seed-borne fungi obtained from seeds of native populations of Iranian cumin (Cuminum cyminum L.), their effect on germination and vigor indices, the location of fungi in seeds and their transmission into seedlings. Based on morphological and molecular characters, the fungi were identified as Alternaria alternata, A. burnsii, Fusarium oxysporum and F. solani. Most of the identified isolates were present in the seed coat, while a few isolates of A. alternata was located in embryos. The results revealed that a negative correlation were found between incidences of naturally fungi infected seed, germination, and vigor indices. The pathogenicity test revealed that 20% of the isolates were non-pathogenic and other isolates were pathogenic or weakly pathogenic. In addition, the percentage seed transmission of fungal phytopathogens to cumin seedlings revealed that A. alternata was the more frequently isolated (67.27%) followed by F. oxysporum (52.80%), A. burnsii (32.74%) and F. solani (20.01%). Then, we investigated correlation among the activities of cell wall degrading enzymes (CWDEs) produced by fungal isolates and variation in pathogenicity and aggressiveness in vivo. Different levels of pathogenicity and aggressiveness were observed for various isolates of Fusarium and Alternaria species. Analysis of CWDEs activities, including cellulase, xylanase, pectinase and lipase showed that cellulase and lipase activities were more important than xylanase and pectinase activities for the pathogenicity of isolates. Therefore, these findings suggested that activity levels of cellulase and lipase are correlated with variation in pathogenicity and aggressiveness of seed-borne fungal isolates on seedling. This is the first report on isolation and identification of seed-borne fungi infection of cumin, together with investigating association between pathogenesis and CWDEs production by isolates isolated from seeds of Iranian cumin native populations. It is also the first time that the location of fungi in seeds and its seed-transmitted into cumin seedlings have been identified and evaluated, respectively.