William R. Meredith

RFLP genetic linkage maps from four F2.3 populations and a joinmap of Gossypium hirsutum L.

Abstract An RFLP genetic linkage joinmap was constructed from four different mapping populations of cotton (Gossypium hirsutum L.). Genetic maps from two of the four populations have been previously reported. The third genetic map was constructed from 199 bulk-sampled plots of an F2.3 (HQ95–6×’MD51ne’) population. The map comprises 83 loci mapped to 24 linkage groups with an average distance between markers of 10.0 centiMorgan (cM), covering 830.1 cM or approximately 18% of the genome. The fourth genetic map was developed from 155 bulk-sampled plots of an F2.3 (119– 5 sub-okra×’MD51ne’) population. This map comprises 56 loci mapped to 16 linkage groups with an average distance between markers of 9.3 cM, covering 520.4 cM or approximately 11% of the cotton genome. A core of 104 cDNA probes was shared between populations, yielding 111 RFLP loci. The constructed genetic linkage joinmap from the above four populations comprises 284 loci mapped to 47 linkage groups with the average distance between markers of 5.3 cM, covering 1,502.6 cM or approximately 31% of the total recombinational length of the cotton genome. The linkage groups contained from 2 to 54 loci each and ranged in distance from 1.0 to 142.6 cM. The joinmap provided further knowledge of competitive chromosome arrangement, parental relationships, gene order, and increased the potential to map genes for the improvement of the cotton crop. This is the first genetic linkage joinmap assembled in G. hirsutum with a core of RFLP markers assayed on different genetic backgrounds of cotton populations (Acala, Delta, and Texas plain). Research is ongoing for the identification of quantitative trait loci for agronomic, physiological and fiber quality traits on these maps, and the identification of RFLP loci lineage for G. hirsutum from its diploid progenitors (the A and D genomes).

Dry matter production, nutrient uptake, and growth of cotton as affected by potassium fertilization

Abstract Insufficient potassium (K) nutrition produces detrimental effects on cotton (Gossypium hirsutum L.) lint yield and fiber quality. To further understand the deleterious effects caused by K deficiency, a 2‐yr (1991 and 1992) field study was conducted to determine how dry matter partitioning and nutrient concentrations of various plant tissues for the cotton genotypes, ‘DES 119’ and ‘MD 51 ne’, were altered by varying the application rate of fertilizer K and nitrogen (N). All plots received a preplant application of 112 kg N ha‐1, and half of the plots were later sidedressed with an additional 38 kg N ha‐1. Within each N treatment, half the plots received 112 kg K ha‐1, preplant incorporated, with the remaining plots not receiving any fertilizer K. Dry matter harvests were taken three times in 1991 and two times in 1992. At cutout (slowing of vegetative growth and flowering), plants that received K fertilization had a 14% more leaf area index (LAI), a 3% increase in the number of main stem nodes, an...

An RFLP linkage map of Upland cotton, Gossypium hirsutum L.

Abstract Ninety-six F2.F3 bulked sampled plots of Upland cotton, Gossypium hirsutum L., from the cross of HS46×MARCABUCAG8US-1-88, were analyzed with 129 probe/enzyme combinations resulting in 138 RFLP loci. Of the 84 loci that segregated as co-dominant, 76 of these fit a normal 1 :  2 : 1 ratio (non-significant chi square at P=0.05). Of the 54 loci that segregated as dominant genotypes, 50 of these fit a normal 3: 1 ratio (non-significant chi square at P=0.05). These 138 loci were analyzed with the MAPMAKER∖ EXP program to determine linkage relationships among them. There were 120 loci arranged into 31 linkage groups. These covered 865 cM, or an estimated 18.6% of the cotton genome. The linkage groups ranged from two to ten loci each and ranged in size from 0.5 to 107 cM. Eighteen loci were not linked.

Near-isogenic cotton germplasm lines that differ in fiber-bundle strength have temporal differences in fiber gene expression patterns as revealed by comparative high-throughput profiling

Gene expression profiles of developing cotton (Gossypium hirsutum L.) fibers from two near-isogenic lines (NILs) that differ in fiber-bundle strength, short-fiber content, and in fewer than two genetic loci were compared using an oligonucleotide microarray. Fiber gene expression was compared at five time points spanning fiber elongation and secondary cell wall (SCW) biosynthesis. Fiber samples were collected from field plots in a randomized, complete block design, with three spatially distinct biological replications for each NIL at each time point. Microarray hybridizations were performed in a loop experimental design that allowed comparisons of fiber gene expression profiles as a function of time between the two NILs. Overall, developmental expression patterns revealed by the microarray experiment agreed with previously reported cotton fiber gene expression patterns for specific genes. Additionally, genes expressed coordinately with the onset of SCW biosynthesis in cotton fiber correlated with gene expression patterns of other SCW-producing plant tissues. Functional classification and enrichment analysis of differentially expressed genes between the two NILs revealed that genes associated with SCW biosynthesis were significantly up-regulated in fibers of the high-fiber quality line at the transition stage of cotton fiber development. For independent corroboration of the microarray results, 15 genes were selected for quantitative reverse transcription PCR analysis of fiber gene expression. These analyses, conducted over multiple field years, confirmed the temporal difference in fiber gene expression between the two NILs. We hypothesize that the loci conferring temporal differences in fiber gene expression between the NILs are important regulatory sequences that offer the potential for more targeted manipulation of cotton fiber quality.

Establishment of molecular markers and linkage groups in two F2 populations of Upland cotton

Two F2 populations of cotton (Gossypium hirsutum L.) from the crosses of HS46 x MARCABUCAG8US-1-88 (MAR) and HS46 x Pee Dee 5363 (PD5363) were characterized for restriction fragment length polymorphisms (RFLPs) using DNA probes. Seventy-three probe/enzyme combinations were used in the HS46 x MAR population analysis, which resulted in 42 informative polymorphic fragments. These 42 moleclar markers represented 26 polymorphic loci, which consisted of 15 codominant and 11 dominant (+/-) genotypes. Chi-square analyses of these loci fit expected genotypic ratios of 1∶2∶1 and 3∶1, respectively An analysis of these loci with the MAPMAKER program resulted in the establishment of four linkage groups A, B, C, and D with 4,2,2, and 2 loci, respectively, as well as 16 unlinked loci. Six probe-enzyme combinations were assayed on the HS46 x PD5363 population, which resulted in 11 informative polymorphic fragments. These 11 fragments represented 6 polymorphic loci, 1 dominant (+/-) and 5 codominant genotypes. The MAPMAKER analysis of these loci yielded 2 linked loci. Thus, a total of 53 polymorphic fragments and 32 polymorphic loci, representing five linkage groups, were identified among the two families.

Production of mRNA from the cry1Ac transgene differs among Bollgard® lines which correlates to the level of subsequent protein

Commercial cultivars of Bollgard® cotton, Gossypiumhirsutum L., differ in the amount of expressed Cry1Ac protein. However, the plant-mechanism for which this occurs is still unknown. Using quantitative real-time polymerase chain reaction (qPCR), we developed a method to determine if differences in the overall level of Cry1Ac among Bollgard® lines could be correlated to the mRNA transcripts. Our data shows that the cry1Ac mRNA transcript differs among Bollgard® lines and are correlated with corresponding Cry1Ac protein levels. In addition, qPCR based methods can efficiently be employed to quantify Cry1Ac protein expression levels in transgenic cotton cultivars. We postulate that qPCR based methods could be successfully employed for quantifying expression levels of transgenes in plants carrying different Bt toxins.

An Assessment ofα‐Tubulin Isotype Modification in Developing Cotton Fiber

Multiple isoforms of α‐ and β‐tubulin accumulate in higher plant cells, including cotton (Gossypium hirsutum L.) fiber. Isotypes may originate either by transcription of distinct genes or by posttranslational modification of gene products. The existence of two types of posttranslational modification in cotton fiber α‐tubulin has been examined by immunoblotting cotton fiber proteins from two developmental stages and by probing with specific monoclonal antibodies to acetylated (6‐11B‐1) or tyrosinated (YL 1/2 ) α‐tubulin. Control experiments were conducted with an antibody (YOL 1/34) that recognizes a conserved region in plant and animal α‐tubulins. No acetylated forms of α‐tubulin were found in either of two varieties of cotton fiber at 10 or 20 d postanthesis. One isotype of α‐tubulin, isotype 6, failed to cross‐react with YL 1/2 at 10 d postanthesis, which indicated that the protein was detyrosinated, and isotype 8 appeared to be detyrosinated at 20 d postanthesis. Since the carboxyl terminus of higher plant α‐tubulin is exposed on the surface of microtubules, removal of the carboxyl‐terminal amino acid may lead to some of the changes in the structure and organization of microtubules that are associated with fiber development.

Effects of Furrow Irrigation on Corn in the Humid Sub-tropical Mississippi Delta

Corn (Zea mays L.) production in the Mississippi Delta has nearly doubled since 1990 but is more susceptible to aflatoxin and fumonisin contamination when grown under drought. Four corn hybrids -- two Bt and two non-Bt -- were grown at Stoneville, MS under irrigated and non-irrigated treatments in 1999, 2000, and 2001. Furrow irrigation was applied at a rate of 1 inch per application during growth stages R1, R3, and R5 in 1999, R1 in 2000, and R1 and R3 in 2001. Irrigation increased grain yields in 2 out of 3 years. More irrigation treatments in 2000 and 2001 would have likely benefited yields. Yields in 2000 were lower than comparable treatments in 1999 and 2001 due to less weight per kernel indicating drought stress occurred during later reproductive growth (R4 to black-layer). Kernel weights were generally higher in both irrigated and non-irrigated treatments in 2001 than they were in 1999 or 2000. This compensated for having fewer kernels per ear, which likely resulted from drought stress at growth stage V12 in 2001. Differences in test weights were observed among years but not irrigation treatments. The Bt hybrids did not differ from the non-Bt hybrids in yield or mycotoxin levels. Aflatoxin and fumonisin contamination did not differ among years or irrigation treatments. Levels were below maximum acceptable concentrations for both mycotoxins. The hybrid N79-L3 had significantly lower fumonisin levels than the other hybrids.

Leaf area index response of four obsolete and four modern cotton cultivars to two nitrogen levels

Abstract The optimal nitrogen (N) rate for cotton (Gossypium hirsutum L.) production in the late 20th century is greater than it was in the middle of the century (112 versus 27 kg ha‐1). Part of the reason for this difference is that modern cultivars exhibit a greater harvest index than obsolete cultivars. This greater harvest index helps to allow modern cultivars to utilize greater N rates. However, factors other than harvest index, such as the development of leaf area in response to N, may also play an important role. Therefore, the objective of this study was to characterize leaf area index (LAI) of four obsolete and four modern cultivars at a low and high fertilizer N level. Cotton was grown in the field for two years (1992 and 1993) with two locations each year. The locations were a Beulah fine sandy loam and a Dubbs silt loam. Two preplant fertilizer‐N rates were used, a low (22 kg N ha‐1) and a high(112 kg N ha‐1). Leaf area index was determined at three stages in each year (early, mid, and late se...

Corn Yields Benefit in Rotations with Cotton

Continuous cotton (Gossypium hirsutum L.) was the primary crop for the Mississippi Delta until recently. Corn (Zea mays L.) is now grown on about 1 million acres in Arkansas, Mississippi, and Louisiana, usually in rotation with cotton. This research evaluated corn’s performance in a four-year furrow irrigated rotation with cotton at Stoneville, MS. The experimental design was a randomized complete block with a split-plot arrangement of treatments replicated eight times. Whole plots were cropping sequences assigned at random. Cropping sequences were continuous cotton, continuous corn, corn-cotton-corn-cotton, or cotton-corncorn-cotton. Four adapted corn hybrids and cotton cultivars were grown as subplots beginning in 2000 to 2003. Corn grain yields were greater following cotton than continous corn in 2001 (169 bu/acre vs. 160 bu/acre) and 2002 (126 bu/acre vs. 117 bu/acre). Grain yields from continuous corn differed among years but with no consistency. Hybrids differed in yield among all years but no consistency in these data was noted. Test weights for continuous corn differed among years but were not below the requirement for US No. 2 yellow corn. Weights of 100 kernels did not differ among years or treatments. Economics dictate cropping sequences but corn can benefit from following cotton in rotation.