Steven D. Linscombe

Rice (Oryza sativa) and Corn (Zea mays) Response to Simulated Drift of Glyphosate and Glufosinate1

Field research was conducted during 3 yr to evaluate response of rice and corn to simulated drift rates representing 12.5, 6.3, 3.2, 1.6, and 0.8% of the usage rates of 1,120 g ai/ha glyphosate (140, 70, 35, 18, and 9 g/ha, respectively) and 420 g ai/ha glufosinate (53, 26, 13, and 4 g/ha, respectively). Early-postemergence applications were made to two- to three-leaf rice and six-leaf corn, and late-postemergence applications to rice at panicle differentiation and to corn at nine-leaf stage (1 wk before tasseling). Crop injury was generally greater for the two highest rates of both herbicides when applied early. Little to no reduction in rice or corn height was observed with glufosinate. Glyphosate consistently reduced rice plant height when the two highest rates were applied early, and heading was delayed 2 to 5 d. In 2 of 3 yr, the highest rate of glyphosate reduced rice yield 99 and 67% when applied early and 54 and 29% when applied late. Germination of rice seeds from glyphosate-treated plants was reduced in 1 of 2 yr and for only the highest rate. For glufosinate, rice yield was reduced 30% and in only one year when applied late at the highest rate. Early application of glyphosate reduced corn yield an average of 22 to 78% for the three highest rates, but only for the highest rate at the late timing (33%). Corn yield was reduced an average of 13 and 11% for the highest rate of glufosinate at the early and late timings, respectively. In greenhouse studies, five rice varieties were equally sensitive, as were five corn varieties, to reduced rates of glyphosate and glufosinate. Nomenclature: Glufosinate; glyphosate; corn, Zea mays L. ‘Asgrow 897’, ‘Dekalb 687’, ‘Mycogen 8460’, ‘Pioneer 3223’, ‘Terral 2930’; rice, Oryza sativa L. ‘Bengal’, ‘Cocodrie’, ‘Cypress’, ‘Drew’, ‘Jefferson’. Additional index words: Crop injury, herbicide drift, off-target movement, rice germination, rice vigor. Abbreviations: DAP, days after plating; DAT, days after treatment.

Identification of Rice Cultivars Resistant to Lissorhoptrus oryzophilus (Coleoptera: Curculionidae), and Their Use in an Integrated Management Program

Abstract The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is the most destructive insect pest of rice in the United States and is a particularly severe pest in Louisiana. The current management program for this insect in Louisiana relies heavily on insecticides, most notably the seed treatment fipronil (Icon). Diversification of the management program by incorporation of alternative strategies is needed to improve the effectiveness and long-term stability of the program. In the three experiments reported here, three components of a diversified management program for the rice water weevil in Louisiana—host plant resistance, treatment of seeds with Icon, and the cultural practice of delayed flooding—were investigated. Comparison of the densities of weevil larvae on the roots of several commercial cultivars indicated that the long-grain cultivar ‘Jefferson’ was more resistant to infestation by the rice water weevil than the other cultivars. The medium-grain cultivars ‘Bengal’, ‘Earl’ and ‘Mars’ and the long-grain variety ‘Cocodrie’ were the most susceptible to infestation. Comparison of yield data from untreated plots and plots treated with Icon indicated that the long-grain cultivars Cocodrie, Lemont, and Jefferson were more tolerant of weevil injury than the other cultivars. A 2-wk delay in flooding was associated with yield benefits in plots not treated with Icon. Treatment of seeds with Icon controlled weevils in all three screening experiments. The implications of these results for the development of an integrated management program for the rice water weevil are discussed.

Genetic variation in Southern USA rice genotypes for seedling salinity tolerance.

The success of a rice breeding program in developing salt tolerant varieties depends on genetic variation and the salt stress response of adapted and donor rice germplasm. In this study, we used a combination of morphological and physiological traits in multivariate analyses to elucidate the phenotypic and genetic variation in salinity tolerance of 30 Southern USA rice genotypes, along with 19 donor genotypes with varying degree of tolerance. Significant genotypic variation and correlations were found among the salt injury score (SIS), ion leakage, chlorophyll reduction, shoot length reduction, shoot K+ concentration, and shoot Na+/K+ ratio. Using these parameters, the combined methods of cluster analysis and discriminant analysis validated the salinity response of known genotypes and classified most of the USA varieties into sensitive groups, except for three and seven varieties placed in the tolerant and moderately tolerant groups, respectively. Discriminant function and MANOVA delineated the differences in tolerance and suggested no differences between sensitive and highly sensitive (HS) groups. DNA profiling using simple sequence repeat markers showed narrow genetic diversity among USA genotypes. However, the overall genetic clustering was mostly due to subspecies and grain type differentiation and not by varietal grouping based on salinity tolerance. Among the donor genotypes, Nona Bokra, Pokkali, and its derived breeding lines remained the donors of choice for improving salinity tolerance during the seedling stage. However, due to undesirable agronomic attributes and photosensitivity of these donors, alternative genotypes such as TCCP266, Geumgangbyeo, and R609 are recommended as useful and novel sources of salinity tolerance for USA rice breeding programs.

Effect of Cultural Practices on Weed Control and Crop Response in Imidazolinone-Tolerant Rice1

Field research was conducted for 3 yr to evaluate crop response and weed control under conventional and reduced tillage in drill- and water-seeded imidazolinone-tolerant (IT) rice culture. Imazethapyr was applied at 70 g ai/ha PRE followed by (fb) imazethapyr at 70 g/ha applied POST to three- to four-leaf rice or at 105 g/ha PRE fb 70 g/ha POST. In both conventional and reduced tillage systems, imazethapyr applied PRE fb POST at 70 g ai/ha controlled red rice, barnyardgrass, Amazon sprangletop, and rice flatsedge 87 to 99% 35 d after POST treatment (DAT). At 35 DAT, Indian jointvetch control with sequential applications of imazethapyr was as high as 70% in water-seeded rice but no more than 54% in drill-seeded rice. Tillage, seeding method, and imazethapyr rate had no effect on days to 50% heading, seeds per panicle, seed weight per panicle, or percentage of seed harvest. However, a reduction of 27% in days to 50% heading, 80% in seeds per panicle, 84% in seed weight per panicle, and 100% in percentage seed harvest index occurred when imazethapyr was not applied because of weed interference. Culm number was reduced 28%, and culm weight 32% under reduced tillage compared with conventional tillage. With sequential applications of imazethapyr at 70 g/ha, rice yield was 63% greater when rice was water-seeded compared with drill-seeded. No differences in tillage systems for weed control, days to 50% heading, seed number, seed weight per panicle, percent seed, panicle height, lodging, or yield were observed. Results of these experiments demonstrate imazethapyr will effectively control weeds in both water- and drill-seeded rice and that reduced tillage can be used without negatively affecting rice production. Nomenclature: Imazethapyr; Amazon sprangletop, Leptochloa panicoides (Presl) Hitchc. #3 LEFPA; barnyardgrass, Echinochloa crus-galli (L.) Beauv. # ECHCG; Indian jointvetch, Aeschynomene indica L. # AESIN; red rice, Oryza sativa L. # ORYSA; rice flatsedge, Cyperus iria L. # CYPIR; rice, Oryza sativa L. ‘93-AS-3510’, ‘CL121’. Additional index words: Conventional tillage, crop injury, drill-seeded rice, reduced tillage, water-seeded rice. Abbreviations: ALS, acetolactate synthase (E.C.4.1.3.18).

Corn and Rice Response to Simulated Drift of Imazethapyr Plus Imazapyr1

Field research was conducted for 2 yr to evaluate response of corn and rice to simulated drift rates of a commercial premix of imazethapyr plus imazapyr [3:1 (w/w)]. Drift rates of the imazethapyr plus imazapyr premix represented 0.8, 1.6, 3.2, 6.3, and 12.5% of the usage rate of 63 g ai/ha (0.5, 1, 2, 4, and 7.9 g/ha, respectively). The imazethapyr plus imazapyr premix applied to six-leaf corn at 7.9 g/ha reduced height 11% compared with the nontreated control 7 days after treatment (DAT) but did not affect corn height 14 and 28 DAT. Corn yield was equivalent regardless of imazethapyr plus imazapyr rate and ranged from 10,200 to 11,500 kg/ha. At 28 DAT, rice height was reduced 12% when 7.9 g/ha of the imazethapyr plus imazapyr premix was applied early postemergence (EPOST) at two- to three-leaf and 14 and 5% when the imazethapyr plus imazapyr premix at 7.9 and 4 g/ha, respectively, was applied late postemergence (LPOST) at panicle differentiation. Reductions in mature rice height of 11 and 6% were observed when the imazethapyr plus imazapyr premix was applied LPOST at 7.9 and 4 g/ha, respectively, and a 5% reduction was observed for 7.9 g/ha of the imazethapyr plus imazapyr premix applied EPOST. Application of the imazethapyr plus imazapyr premix EPOST at 7.9 g/ha delayed heading in only 1 yr, but heading was delayed both years when applied LPOST. Rice yield was reduced 39 and 16% when the imazethapyr plus imazapyr premix was applied LPOST at 7.9 and 4 g/ha, respectively, compared with a 9% yield reduction for 7.9 g/ha applied EPOST. Nomenclature: Imazapyr; imazethapyr; corn, Zea mays L. ‘Dekalb 687’; rice, Oryza sativa L. ‘Cypress’. Additional index words: Crop injury, herbicide drift, off-target movement. Abbreviations: IR, imidazolinone-resistant.

Identification and validation of QTLs for seedling salinity tolerance in introgression lines of a salt tolerant rice landrace ‘Pokkali’

Salinity is a major threat to rice production worldwide. Several studies have been conducted to elucidate the molecular basis of salinity tolerance in rice. However, the genetic information such as quantitative trait loci (QTLs) and molecular markers, emanating from these studies, were rarely exploited for marker-assisted breeding. To better understand salinity tolerance and to validate previously reported QTLs at seedling stage, a set of introgression lines (ILs) of a salt tolerant donor line ‘Pokkali’ developed in a susceptible high yielding rice cultivar ‘Bengal’ background was evaluated for several morphological and physiological traits under salt stress. Both SSR and genotyping-by-sequencing (GBS) derived SNP markers were utilized to characterize the ILs and identify QTLs for traits related to salinity tolerance. A total of eighteen and thirty-two QTLs were detected using SSR and SNP markers, respectively. At least fourteen QTLs detected in the RIL population developed from the same cross were validated in IL population. Analysis of phenotypic responses, genomic composition, and QTLs present in the tolerant ILs suggested that the mechanisms of tolerance could be Na+ dilution in leaves, vacuolar Na+ compartmentation, and possibly synthesis of compatible solutes. Our results emphasize the use of salt injury score (SIS) QTLs in marker-assisted breeding to improve salinity tolerance. The tolerant lines identified in this study will serve as improved breeding materials for transferring salinity tolerance without the undesirable traits of Pokkali. Additionally, the lines will be useful for fine mapping and map-based cloning of genes responsible for salinity tolerance.

Genetic Dissection of Seedling Stage Salinity Tolerance in Rice Using Introgression Lines of a Salt Tolerant Landrace Nona Bokra

Salinity is an important abiotic stress affecting rice production worldwide. Development of salt tolerant varieties is the most feasible approach for improving rice productivity in salt affected soils. In rice, seedling stage salinity tolerance is crucial for better crop establishment. Quantitative trait loci (QTL) mapping using introgression lines (ILs) is useful for identification and simultaneous transfer of desirable alleles into elite genetic background. In the present study, 138 ILs derived from the cross between a high yielding elite salt susceptible japonica rice cultivar Jupiter and a salt tolerant indica landrace Nona Bokra were evaluated for salt tolerance at seedling stage in a hydroponics experiment and were genotyped using 126 simple sequence repeat markers. A total of 33 additive QTLs were detected by composite interval mapping for 8 morphophysiological traits. The phenotypic responses, genomic composition, and QTLs identified from the study indicated that Na/K ratio is the key factor for salinity tolerance. The mechanisms of tolerance might be due to homeostasis between Na+ and K+ or Na+ compartmentation. Gene ontology (GO) analysis revealed that significant GO terms in the selected QTL regions were associated with the genes/pathways involved in signaling, enzyme inhibition, and ion transport. Because majority of QTLs are with small effects, marker-assisted recurrent selection is proposed to accumulate favorable alleles for improving salt tolerance using the tolerant ILs identified in this study. The tolerant ILs also provide an opportunity for functional genomics studies to provide molecular insights into salt tolerance mechanisms in Nona Bokra.

Transgene Transfer to United States Commercial Rice Cultivars via Conventional Breeding Techniques

Abstract Breeding programs can benefit from transfer of a foreign gene from one transgenic plant to commercial cultivars through continuous backcrossing, especially to cultivars in which it is difficult to transfer a foreign gene directly through biotechnology. In this study, two homogeneous transgenic plants, T-28 and T-64 (from Taipei 309), and one homogeneous transgenic plant, N-84 (from Nipponbare), were used as donors of Bar gene. Commercial cultivars, Cypress and Laffite, were used as the recurrent parents. Three to five backcrosses were made using the transgenic plants as donor parents and the commercial cultivars as recurrent parent. The results from selected progeny rows, and two-years of yield tests with selected lines, indicated that the target Bar gene could be transferred to lines from homozygous transformants in 2–3 years of backcrossing, giving lines similar to the recurrent parents in phenotype and yield potential.

Clonal Variation in Cereals and Forage Grasses

Clonal changes in tissue culture have proved to be a useful method for creating desirable variants in most cereal crops. Variants include changes in physiological mechanisms, agronomic characteristics, plant type, and resistance to pests and stress conditions.

Visual Estimation of Rice (Oryza sativa L.) Grain Yield in Multiple Environments in Louisiana

Development of high-yielding rice (Oryza sativa L.) cultivars is a primary objective of most rice-breeding programs, and breeding progress is generally measured through increases in grain yield attributable to new cultivars. The pedigree-breeding method, commonly employed in rice-breeding programs, usually results in a large number of lines being discarded in early generations on the basis of visual estimates of grain yield potential. The objective of this research, conducted at five locations in 2007 and 2008 in Louisiana, was to evaluate the effectiveness of visual grain-yield predictions by two rice breeders. A second objective was to determine the effect of disease and lodging on the accuracy of visual selection. Across all years and locations, the grain yield estimates of both breeders were positively correlated with observed grain yield, indicating that visual selection for grain yield can be effective. Differences existed in the predictive ability of the breeders to estimate grain yield at different environments. Generally, breeders were more accurate in visually estimating grain yield when the standard deviation of the estimates was high, indicating that perceived phenotypic expression of grain yield is an important factor affecting the visual estimation of yield potential. Locations with high disease pressure and lodging resulted in a greater standard deviation of the yield estimates and improved the accuracy of visual estimation of grain yield.