Evaluation of Cotton Cultivars and Breeding Lines for Tolerance to Monosodium Methanearsonate (MSMA) Under Field Conditions.

Monosodium methanearsonate (MSMA) is an organic arsenical herbicide used to control weeds such as grasses and nutsedges in Upland cotton (Gossypium hirsutum) production. Transient crop injury, yield reduction, and maturity delays have been observed in commercial Upland cotton. It is unknown if genetic variation in MSMA tolerance in cotton exists. In this field study, seven replicated tests were conducted in the same field to compare MSMA tolerance among 212 commercial cotton cultivars and advanced breeding lines. The tests were sprayed over the top at the 4-true-leaf stage, and seedlings were assessed for crop injury severity on a scale of 0 (no injury) to 5 (death). Significant genotypic variation in MSMA tolerance was detected in three tests, and broad-sense heritability estimates for MSMA tolerance ranged from 0.476 to 0.846 with a mean of 0.712, indicating that most phenotypic variation in MSMA tolerance is heritable. Nine tested G. barbadense genotypes, including seven commercial Pima cultivars and two Sea-Island cotton lines, exhibited minimal crop injury with severity ratings of 0.40 to 0.83 (except for one cultivar with 1.33). Among the remaining 203 Upland cotton genotypes with crop injury ratings ranging from 0.90 to 3.67, five commercial transgenic cultivars and 38 public breeding lines exhibited various levels of MSMA tolerance. The results represent the first study in germplasm evaluation for MSMA tolerance and identify a set of tolerant cotton genotypes that can be selected in cotton production or used to develop new cultivars for commercial cotton production. [ABSTRACT FROM AUTHOR]