Evaluation of rotation varieties strategies to control reniform nematode in cotton (Gossypium hirsutum L.)

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Rotylenchulus reniformis (Hoplolaimidae), is one of the most important pathogens associated with cotton (Gossypium hirsutum L.) yield losses in Texas. In the United States, currently 17 states are producers of cotton (Gossypium spp.), with Texas being the main producer. Approximately 60 % of the total production in the United States is produced in Texas. Two common practices for managing nematodes are crop rotation and the use of nematode-resistant varieties. Although there are many reports of the benefits of rotating cotton with non-host crops such as corn (Zea mays), sorghum (Sorghum spp.), peanuts (Arachis hypogaea), there are producers who practice monoculture. For this reason, the effect on nematode populations has been studied when rotating with resistant varieties that allow their populations to decrease. Recently, in 2021, two companies released cotton varieties resistant to the Reniform nematode. Therefore, the objective of this investigation was to evaluate the effect of variety rotation (resistant and susceptible) and weed-free fallow on R. reniformis populations in West Texas. The experiment was conducted from 2020 to 2022 in field 405 at the Texas A&M AgriLife Research and Extension Center in Lubbock, Texas. Nine treatment combinations were selected to evaluate the efficiency of rotation varieties on the RN population. The combination of nine treatments was RRR, SSS, RSR, RRS, RSS, FSF, FSS, FFS, FRS (1st letter= 2020, 2nd = 2021, 3rd = 2022), where R= Resistant variety (DP 2143NR B3XF), S = Susceptible variety (DP 2044 B3XF), and F= Weed-free fallow. A randomized complete block design (RCBD) was used with 4 replicates for a total of 36 plots per year. Pie Pan method were used to collect the vermiform reniform nematode. Each sample was composed of ten soil subsamples. The identification of RN was confirmed using the pictorial key of plant-parasitic nematodes. The yield (kg of lint/ha) was collected by combination of treatments every year. The initial population of RN was determined in the year 2020, prior to the effect of the treatments, and on average 926 RN/100 cm3 soil were counted. Three months before harvest, the population in the resistant variety, susceptible variety, and weed-free fallow was 439 RN/100 cm3 soil, 1,025 RN/100 cm3 soil, and 288 RN/100 cm3 soil, respectively. Six combinations were evaluated in the year 2021 (RR, SS, FF, RS, FR, FS). The populations in the FF treatment (60 RN/100 cm3 soil) were the lowest, followed by the RR treatment (280 RN/100 cm3 soil). An increase of 34 % is observed in the populations of the SS treatment (835 RN/100 cm3 soil). The evaluation of the nine rotations was completed in 2022, where the lowest populations were reported in the RRR treatment. The order of efficacy of the treatments was as follows: FSF, FFS, RSR, FRS, FSS, SSS, RSS, and RRS (lowest to highest RN population). During the three years, the susceptible variety maintained its populations. By the year 2020, the highest yields were associated with the resistant variety. In 2021, the highest yield was associated with RR (916 kg of lint/ha), followed by FR (815 kg of lint/ha). A significant decrease was observed in the SS treatment (516 kg of lint/ha). In 2022, the highest yields were associated with the RRR treatment (1,271 kg of lint/ha), monoculture with the resistant variety. The second treatment with the highest yield was RSR (1,051 kg of lint/ha). As expected, the lowest yields were observed in rotations with the susceptible variety SSS (597 kg of lint/ha) and RSS (599 kg of lint/ha). The resistance of the variety DP 2143NR B3XF was observed in all the years of rotation. This variety or strategy of using reniform nematode resistant cultivars represents an effective alternative for producers to crop rotation or fallowing the land. Other treatments such as RSR could represent an opportunity to obtain appropriate yields, compared to SSS, and avoid the development of resistance of this pathogen to cotton. Future studies are important to evaluate the consistency of the results obtained in RSR and in the treatments that were rotated with Weed-free fallow (F), since the yield was affected.

Rotylenchulus reniformis, reniform nematode, Gossypium hirsutum, Upland cotton, nematode disease