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

Abstract

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 controlledconditions 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.

Targeted development of diagnostic SNP markers for resistance to Fusarium wilt race 4 in Upland cotton (Gossypium hirsutum)

“…Among the three evaluation parameters in Set 1, MR was significantly but weakly correlated with SVD (r= 0.291, P<0.01) and RVD (r= 0.169, P<0.05); however, SVD and RVD was highly significantly correlated (r= 0.712, P<0.0000), consistent with our previous reports (Zhang et al 2022b;Zhu et al 2023b). In this test, ANOVA detected significant differences in responses (MR, SVD and RVD) to FOV4 infections, warranting a further analysis between the three evaluation parameters and SNP markers.…”

“…Once adequate seeds from these germplasm lines are obtained, they will be further evaluated for FOV4 resistance under field (Fabens, Texas) conditions and made publicly available. Based on a set of eight cotton cultivars, we (Zhang et al 2022b, c, f) previously demonstrated that evaluation results for FOV4 resistance in the greenhouse were consistent with these under the field (Fabens, Texas) conditions, but with a lower experimental errors.…”

“…Because of the uniqueness of FOV4, resistance to seedling damping-off caused by FOV4 requires a different genetic mechanism in cotton. Previously, we showed that seedling mortality caused by FOV4 was correlated with SVD and RVD, but the associations were far from perfect (Zhang et al 2022b; Zhu et al 2023b), suggesting both common and independent resistant mechanisms for MR and vascular discoloration.…”

“…However, no DNA markers associated with the resistance in these resistant lines and cultivars have been identified. Building on our previous studies in establishing a reliable screening method for FOV4 resistance in cotton (Zhang et al 2020b, 2021, 2022a, b, c; Zhu et al 2021b, 2022, 2023), the objective of this study was to develop the first set of SNP markers associated with FOV4 resistance in Upland cotton. The results will facilitate more molecular genetic studies which will accelerate the development of FOV4-resistant Upland cotton cultivars and cloning and isolation of the underlying resistance genes.…”

Effect of growth stage, cultivar, and root wounding on disease development in cotton caused by Fusarium wilt race 4 (Fusarium oxysporum f. sp. vasinfectum)

“…Therefore, apparent strong resistance responses can be overcome at a high FOV4 density or by a high virulent infection type. Under field conditions, we have observed light root vascular discoloration in a few mature plants from resistant Pima PHY 841 RF and FM 2334GLT due to unknown reasons (Zhang et al., 2022a). It may be due to high FOV4 inoculum density surrounding these plants, even though seed heterogeneity due to natural crossing and segregation cannot be ruled out.…”