RESUMO
A three-year rotation of cotton (Gossypium hirsutum) cultivars either resistant (R) or susceptible (S) to Rotylenchulus reniformis and fallow (F) was examined for effect on cotton yield and nematode density. In year 1, 2, and 3, the resistant cultivar (DP 2143NR B3XF) yielded 78, 77, and 113% higher than the susceptible cultivar (DP 2044 B3XF). Fallow in year 1 followed by S in year 2 (F1S2) improved yield in year 2 by 24% compared with S1S2, but not as much as R1S2 (41% yield increase over S1S2). One year of fallow followed by R (F1R2) had lower yield in year 2 (11% reduction) than R1R2. The highest yield after three years of these rotations occurred with R1R2R3, followed by R1S2R3 (17% less yield) and F1F2S3 (35% less yield). Rotylenchulus reniformis density in soil averaged 57, 65, and 70% lower (year 1, 2, 3, respectively) in R1R2R3 compared with S1S2S3. In years 1 and 2, LOG10 transformed nematode density (LREN) was lower in F1, and F1F2, than for all other combinations. In year 3, the lowest LREN were associated with R1R2R3, F1S2F3, and F1F2S3. The highest LREN were associated with F1R2S3, F1S2S3, S1S2S3, R1R2S3, and R1S2S3. The combination of higher yield and lower nematode density will be a strong incentive for producers to use the R. reniformis resistant cultivars continuously.
RESUMO
Cotton (Gossypium hirsutum) cultivar trials were conducted in four fields (6 trials total) with Meloidogyne incognita (Mi)/Fusarium oxysporum f. sp. vasinfectum (Fov) from 2019 to 2021. Cotton cultivars were divided into groups based on company/Mi resistance: S = susceptible to Mi; R-FM, R-DP, and R-PHY = resistance to Mi in FiberMax®, Deltapine®, and Phytogen® cultivars, respectively; ST 4946GLB2 (moderate resistance to Mi and observed field tolerance to Fov); and ST 5600B2XF (resistance to Mi). The S and R-FM groups had the highest transformed Mi densities LOG10(Mi + 1) (LMi = 3.22 and 3.01, respectively), while R-DP and R-PHY had the lowest LMi (2.21 and 1.85, respectively). Plant mortality (%) was higher for R-DP (28.1%) than for all other groups except ST 5600B2XF (24.8%). Mi-susceptible cultivars averaged 23.3% mortality. Relative yield (0-1 scale) was higher for ST 4946GLB2 (0.706) and R-PHY (0.635) than for R-DP (0.530), ST 5600B2XF (0.578), and S (0.491). All groups except R-DP averaged higher relative yield than the susceptible cultivars. ST 4946GLB2 had the lowest mortality (16.5%) and highest relative yield, while R-DP cultivars had the highest mortality and no difference in relative yield from the Mi-susceptible cultivars. The group of R-DP cultivars had excellent Mi resistance but were susceptible to Fov. No cultivars were identified with high resistance to Fov.
RESUMO
Small plot cotton cultivar trials (12 trials) were conducted from 2016 to 2019 in fields infested with Meloidogyne incognita. Entries in these trials included commercial cultivars with partial and high resistance to M. incognita, as well as cultivars with no known resistance. Different resistant groups were created based on different cotton seed companies and their descriptions of the M. incognita resistant cultivars. Groups were none (susceptible); partial resistance found in Stoneville or Fibermax cultivars (PR-FM/ST); partial resistance found in PhytoGen cultivars (PR-PHY); resistance (unknown gene(s)) in Deltapine cultivars (NR-DP); and highly resistant cultivars homozygous for RK1 and RK2 resistant genes in PhytoGen cultivars (HR-PHY). The highest lint yields using a mixed model analysis were found in the PR-FM/ST (1,396 kg lint/ha), HR-PHY (1,327 kg lint/ha), and PR-PHY (1,314 kg lint/ha) groups. Yield for NR-DP (1,234 kg lint/ha) was not different (p > 0.05) than yield for susceptible cultivars (1,243 kg lint/ha). If the older resistant cultivars from Deltapine and PhytoGen (those with only Roundup Ready® herbicide technology) were removed from the analysis, then HR-PHY yields increased by 133 kg of lint/ha to 1,460 kg lint/ha and NR-DP yields remained approximately unchanged (1,227 kg lint/ha). Newer HR-PHY had much improved yield over the first HR-PHY cultivars. Newer HR-PHY averaged 17% higher yield than the susceptible group. LOG10 (M. incognita eggs/500 cm3 soil + 1) were highest for the susceptible cultivars (3.2), followed by PR-FM/ST (2.6), NR-DP (2.4), PR-PHY (2.1), and lowest with HR-PHY (1.4). The newer HR-PHY cultivars (those with ENLIST® herbicide technology) combine excellent yields (17% higher than susceptible cultivars) with high (96%) suppression of M. incognita.Small plot cotton cultivar trials (12 trials) were conducted from 2016 to 2019 in fields infested with Meloidogyne incognita. Entries in these trials included commercial cultivars with partial and high resistance to M. incognita, as well as cultivars with no known resistance. Different resistant groups were created based on different cotton seed companies and their descriptions of the M. incognita resistant cultivars. Groups were none (susceptible); partial resistance found in Stoneville or Fibermax cultivars (PR-FM/ST); partial resistance found in PhytoGen cultivars (PR-PHY); resistance (unknown gene(s)) in Deltapine cultivars (NR-DP); and highly resistant cultivars homozygous for RK1 and RK2 resistant genes in PhytoGen cultivars (HR-PHY). The highest lint yields using a mixed model analysis were found in the PR-FM/ST (1,396 kg lint/ha), HR-PHY (1,327 kg lint/ha), and PR-PHY (1,314 kg lint/ha) groups. Yield for NR-DP (1,234 kg lint/ha) was not different (p > 0.05) than yield for susceptible cultivars (1,243 kg lint/ha). If the older resistant cultivars from Deltapine and PhytoGen (those with only Roundup Ready® herbicide technology) were removed from the analysis, then HR-PHY yields increased by 133 kg of lint/ha to 1,460 kg lint/ha and NR-DP yields remained approximately unchanged (1,227 kg lint/ha). Newer HR-PHY had much improved yield over the first HR-PHY cultivars. Newer HR-PHY averaged 17% higher yield than the susceptible group. LOG10 (M. incognita eggs/500 cm3 soil + 1) were highest for the susceptible cultivars (3.2), followed by PR-FM/ST (2.6), NR-DP (2.4), PR-PHY (2.1), and lowest with HR-PHY (1.4). The newer HR-PHY cultivars (those with ENLIST® herbicide technology) combine excellent yields (17% higher than susceptible cultivars) with high (96%) suppression of M. incognita.
