Studies of evaluation parameters for resistance to Fusarium wilt in cotton caused by Fusarium wilt race 4 (Fusarium oxysporum f. sp. vasinfectum)

Fusarium wilt, caused by Fusarium oxysporum f. sp. vasinfectum race 4 (FOV4), is an early season vascular disease with symptoms including seedling wilt and mortality. The objectives of this study were to investigate the relationship between mortality rate (MR) and disease severity rating (DSR) based on root vascular staining (RVS)-DSR and stem vascular discoloration (SVD)-DSR in the field and the relationship of MR in controlled conditions with MR and DSR in the field. Results from two field tests and two greenhouse tests each with a Latin square design for eight cultivars of cotton (Gossypium spp.) and two field progeny-row tests were analyzed. In the field, MR at the square stage was significantly correlated with both DSR (RVS) and DSR (SVD) at crop maturity, and they were also significantly correlated with DSR based on both MR and RVS-DSR (MR+RVS) and both MR and SVD-DSR (MR+SVD). The results show that DSR (MR+RVS) was the most accurate in assessing FOV4 resistance, and DSR (SVD) and DSR (MR+SVD) can be used in combination with DSR (RVS) and DSR (MR+RVS), or as the substitutes for RVS. Mortality rate in the greenhouse was significantly correlated with MR and DSR (MR+RVS) and DSR (MR+SVD) in the field, indicating consistency between evaluations under both conditions. Furthermore, foliar symptoms-based MR and DSR under controlled-conditions were significantly correlated, with coefficients of variation at 20 to 30% in other related studies. The results confirm the validity of using the two parameters in greenhouse evaluations for FOV4 resistance in cotton.