Inheritance of resistance to fenoxaprop‐p‐ethyl in sprangletop ( L eptochloa chinensis L . N ees)

Sprangletop ( L eptochloa chinensis   L . N ees) is a serious grass weed in direct‐seeded rice cropping systems in T hailand. One population of sprangletop, BLC1 , was found to be resistant to fenoxaprop‐p‐ethyl at 62‐fold the concentration of a susceptible biotype, SLC1 . This study elucidated the inheritance of resistance to fenoxaprop‐p‐ethyl in this sprangletop BLC1 genotype. The reaction to the herbicide at 0.12–2.4 mg ai L −1 was determined in the seedlings of self‐pollinated resistant BLC1 , susceptible SLC1 and SLC1 that had been allowed to cross‐pollinate with BLC1 . At 0.24 mg ai L −1 , all the seedlings of SLC1 were killed, while 99% of BLC1 survived, along with 5% of the cross‐pollinated SLC1 seedlings, which were considered to be putative F 1 hybrids. The root and shoot lengths of the F 1 hybrids in 0.24 mg ai L −1 of fenoxaprop‐p‐ethyl, relative to those in the absence of the herbicide, were close to or the same as the resistant parent, indicating that the resistance is a nearly complete to complete dominant trait. One‐hundred‐and‐forty‐one of the F 2 ‐derived F 3 families were classified by their response to the herbicide at 0.24 and 0.48 mg ai L −1 into 39 homozygous susceptible : 72 segregating : 30 homozygous resistant, fitted with a 1:2:1 ratio at χ 2 = 1.21 and P = 0.56, indicating that the resistance to fenoxaprop‐p‐ethyl in the sprangletop BLC1 genotype is controlled by a single gene.