Impact of fumigation on soybean varieties against Rotylenchulus reniformis

The reniform nematode (Rotylenchulus reniformis) is one of the major pests on both soybean and cotton in the southern USA. Yield losses from this nematode to soybean have been reported to be greater than from cotton. Resistance in soybean cultivars against reniform nematode is not consistent with different geographical isolates of the pathogen. Resistant soybean cultivars recommended for Louisiana are based on the evaluations done in Arkansas with their native reniform populations. Field experiments were conducted during 2014-2015 in Tensas parish Louisiana, to evaluate the response of nematicide on 18 soybean cultivars against endemic R. reniformis populations. These soybean cultivars were categorized as susceptible, moderately resistant and resistant, according to studies conducted in Arkansas. In 2014 trial, fumigated (1,3-dichloropropene) and non-fumigated treatments representing 9 cultivars were employed. Nematode population data were collected at-planting, midseason and at-harvest. Application of the nematicide significantly reduced nematode population levels at all three sampling intervals. Out of the 9 cultivars, Delta Grow 4940 and S11-20354 had the lowest reniform nematode populations without fumigation at midseason and at-harvest. The cultivar R04-1268 produced the highest nematode populations in the absence of fumigation at both midseason and at-harvest. In both the presence and absence of the fumigant, lowest yields were observed with R04-1268, MPG 4714N, and Asgrow 4534. In 2015, another 9 soybean cultivars were tested in the same field with and without the fumigant. Similar to 2014, nematode population data were collected at-planting, midseason and at-harvest. Application of the nematicide significantly reduced nematode population levels at all three sampling intervals following a similar trend from the previous year. In this study, Asgrow 5535, Dyna Grow s52RY75 and Delta Grow 5230 had the lowest reniform nematode populations without fumigation at-harvest. The cultivar Delta Grow 5625 produced the highest nematode populations at harvest in nematicide untreated plots and resulted in significantly lower yield. These studies indicated that even with a different reniform isolate, soybean cultivars considered as resistant were able to hold their resistant against a population of reniform nematode in Louisiana

A survey of Aphelenchoides besseyi on rice in Louisiana

Aphelenchoides besseyi, the causal agent of white-tip disease of rice is one of the plant pathogenic nematodes that causes losses in rice production. This nematode has historically been considered a minor pest in the United States but recently has been found in a number of quarantine samples for overseas shipment in both Arkansas and Louisiana. The objective of this study was determine the current distribution of A. besseyi in Louisiana. A survey was conducted using seed samples obtained from the State Seed Testing Laboratory of the Louisiana Department of Agriculture and Forestry. These seeds represent rice cultivars that were grown in Louisiana or imported from out-of-state for sale to farmers for the years 2015 and 2016. The samples were taken to the nematology lab at LSU and 25 gram sub-sample of each sample was analyzed. The sub-samples were blended in water, placed on a Baermann funnel and counted using a microscope after 24 hours. In total, 189 samples were evaluated, representing 25 different cultivars. Among these samples, 21% were from 4 hybrid cultivars imported from out-of-state. Aphelenchoides besseyi was found in 17 samples belonging to 6 cultivars. Fourteen of the infested samples were from the hybrid cultivars of rice. Approximately 83% of the samples from the rice hybrid cultivar XL 729 were infested with A. besseyi. Populations of the nematode ranged from 2 to 288 per 25g of infected rice seed. Most of the infested seed were from long grain types, but 3 of the infested samples were medium grain types. This study would indicate that most of the rice cultivars produced in Louisiana and released to farmers are relatively free of this pest. Future work will be conducted in order to evaluate more cultivars from Louisiana and test their resistance to white-tip nematode

Incidence of Aphelenchoides Besseyi in rice in Louisiana and host status of the most widely planted cultivars

Aphelenchoides besseyi, the causal agent of white tip disease of rice, has been considered a minor pest of rice during the past 50 years in the United States. Recently, this nematode has been found in a number of quarantine samples in Louisiana and Arkansas. The objectives of this research were to determine incidence of this nematode in commercial seed sold to producers in Louisiana and to determine the host status of major rice cultivars currently produced in the state. During 2015-2016, a total of 216 seed samples, representing 3 medium grain, 18 long grain, and 4 long grain hybrid rice cultivars, were examined for A. besseyi. The nematode was detected in 12% of the samples, and the highest incidence occurred on long grain hybrids with 30% of the 63 samples infested. Nineteen-week-duration greenhouse studies were conducted to evaluate reproduction of the nematode and pathogenicity to three medium, three long grain, and three long grain hybrid rice cultivars currently popular in Louisiana. Reproductive values of the nematode ranged from 11.9 to 2.9 for medium grain cultivar Jupiter and long grain hybrid XL 753, respectively. Grain weights of Jupiter, CL 111, and XL 753 rice plants inoculated with A. besseyi were reduced below those of non-inoculated controls (P<0.01). The nematode reduced plant height of all cultivars (P<0.01). Plant weights of Jupiter, CL 111, CL 152, XL 745, and XL 753 were reduced when inoculated with A. besseyi. Germination and seedling growth studies conducted in the laboratory and greenhouse indicated that A. besseyi reduced medium grain Jupiter seed germination by 27% with a decrease in the germination index on 6 of the 9 cultivars evaluated

Reproduction and pathogenicity of endemic populations of Rotylenchulus reniformis on cotton

The reniform nematode (Rotylenchulus reniformis) is the predominant parasitic nematode of upland cotton (Gossypium hirsutum) in the southern United States. Little is known about variability in geographic isolates of reniform nematode. In order to evaluate the comparative reproduction and pathogenicity of reniform nematode populations endemic in Louisiana, a series of microplot and greenhouse experiments were conducted. Reniform nematode populations derived from single-egg masses collected from West Carroll (WC), Rapides (RAP), Morehouse (MOR) , and Tensas (TEN) parishes were used in full-season (150 days) microplot, and 60-day greenhouse experiments, each repeated once. Data from two microplot trials, averaged over 2 yr, showed significant differences among isolates of reniform nematode in both reproduction and pathogenicity on upland cotton cultivars Phytogen 499 WRF, Deltapine 1133 B2RF, and Phytogen 333 WRF. Across all cotton cultivars, the MOR and RAP isolates had the greatest and the least reproduction value of 331.8 and 230.2, respectively. Reduction in plant dry weight, number of bolls, seed cotton weight, and lint weight was the greatest and the least for MOR and RAP isolates, respectively. MOR and RAP isolates lowered plant dry weights of cotton by 55%, and 9%, respectively. Reproduction and pathogenicity of the WC and TEN isolates were intermediate. Data from greenhouse trials showed results similar to that of microplot trials. In greenhouse experiments, reproduction of MOR and RAP isolates across all cotton genotypes was the greatest (reproductive value of 10.7) and the least (reproductive value of 7.9), respectively. Although reproductions of reniform nematode were lower in the germplasm lines than the cultivars, the germplasm lines sustained greater plant weight loss. The variability in reproduction and pathogenicity among endemic populations of reniform nematode in both the microplot and greenhouse experiments adds further support to the hypothesis that virulence phenotypes of R. reniformis exist