Variability Among Ecotypes of Barnyardgrass (Echinochloa Crus-Galli Var. Crus-Galli (L.) Beauv.) and its Susceptibility to Exserohilum Longirostratum

Barnyardgrass (Echinochloa crus-galli var. crus-galli (L.) Beauv) is one of the most noxious weeds found in rice fields of both Malaysia and Indonesia. Its diversity in morphological and molecular traits within and between the regions of Malaysian and Indonesian ecotypes was investigated in this study in relation to its susceptibility to potential biocontrol agent using fungal Exserohilum longirostratum. A total of 85 individual ecotypes found in rice fields of the two countries were characterized. Fifty-five ecotypes from eleven different states in Malaysia and 30 ecotypes from three sub-regions (Sumatera, Java and Sulawesi islands) of Indonesia were collected. iii Morphological (vegetative and reproductive characters) and molecular (RAPDPCR) studies for diversity assessment within and between Malaysian and Indonesian ecotypes were employed. Results from morphological studies indicated that there was variability within the Malaysian and Indonesian ecotypes due to difference in characters such as plant height, panicle awn, panicle length, plant type, and number of tillers with 95.77 and 100% of total variability. To some extent, percent germination, seedling growth characters and life cycles for Malaysian ecotypes from Perlis, Kedah, Perak, Kelantan, and Johor were relatively faster than Indonesian ecotypes from Lampung, Banten, West Java, Central Java, East Java, and South Sulawesi. Molecular (RAPD-PCR) analysis of 26 Malaysian and 14 Indonesian barnyardgrass ecotypes were amplified using four primers (A 07 A 20, OPG 06 and OPAE 12), which amplified a total of 533 and 266 repeatable fragments. The RAPD variation between Malaysian and Indonesian ecotypes ranged from 85.7 to 89% and 67 to 80%. The analysis of genetic similarity revealed four distinct clusters with an average similarity of 47% for Malaysian ecotypes, while 64% for Indonesian ecotypes. The results of the study indicated that the close relationship within and between Malaysian and Indonesian ecotypes were mainly due to the close vicinity in geographic locations. Taking into consideration that the barnyardgrass found in both countries are quite similar in characters. The response of barnyardgrass ecotypes to the virulence of fungal Exserohilum longirostratum, a potential biocontrol agent was evaluated. Results of this study indicated that susceptibility varied for Malaysian and Indonesian ecotypes in glasshouse and mini-plot experiments. Plant growth of 1-2- and 2-3-leaf stages were observed to be the most susceptible growth stage to E. longirostratum at a concentration of 1x107 and 2.5x107 conidia/mL when exposed to 24 hours of dew period. However, seedlings mortality decreased slightly with increase in plant age (4-5- and 6- 7-leaf stages). The most susceptible ecotypes were found in Kedah, Perak, Kelantan, Lampung and Central Java as indicated by the high value of the AUDPC (594 to 641) and high epidemic rate (rL) (0.358 to 0.485 unit/day), while susceptible ecotypes iv iv were found in Melaka, Selangor, Terengganu, Banten and South Sulawesi with AUDPC value of 340 to 387 and epidemic rate (rL) value of 0.193 to 0.254 unit/day. These ecotypes also showed significant increase in seedling mortality (87 to 92%) compared to other ecotypes. These studies have demonstrated differential susceptibility within and between weed population diversity. The results obtained from this study indicated that E. longirostratum has the potential to be used as a mycoherbicide against barnyardgrass ecotypes. However further studies such as increased conidia concentration with different surfactants, formulation, and characterization of phytotoxic compound to enhance the virulence for satisfactory control of barnyardgrass in rice fields conditions are required.

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