Chromosome identities were assigned to 15 linkage groups of the RFLP joinmap developed from four intraspecific cotton (Gossypium hirsutum L.) populations with different genetic backgrounds (Acala, Delta, and Texas Plains). The linkage groups were assigned to chromosomes by deficiency analysis of probes in the previously published joinmap, based on genomic DNA from hypoaneuploid chromosome substitution lines. These findings were integrated with QTL identification for multiple fiber and yield traits. Overall results revealed the presence of 63 QTLs on five different chromosomes of the A subgenome (chromosomes-03, -07, -09, -10, and -12) and 29 QTLs on the three different D subgenome (chromosomes-14 Lo, -20, and the long arm of -26). Linkage group-1 (chromosome-03) harbored 26 QTLs, covering 117 cM with 54 RFLP loci. Linkage group-2, (the long arm of chromosome-26) harbored 19 QTLs, covering 77.6 cM with 27 RFLP loci. Approximately 49% of the putative 92 QTLs for agronomic and fiber quality traits were placed on the above two major joinmap linkage groups, which correspond to just two different chromosomes, indicating that cotton chromosomes may have islands of high and low meiotic recombination like some other eukaryotic organisms. In addition, it reveals highly recombined and putative gene abundant regions in the cotton genome. QTLs for fiber quality traits in certain regions are located between two RFLP markers with an average of less than one cM (approximately 0.4-0.6 Mb) and possibly represent targets for map-based cloning. Identification of chromosomal location of RFLP markers common to different intra- and interspecific-populations will facilitate development of portable framework markers, as well as genetic and physical mapping of the cotton genome.

The development of late‐season K deficiency symptoms in cotton (Gossypium hirsutum L.) fields has become more frequent in the Mid‐South and Far West U.S. production regions. In this study, the objectives were to determine how yield and quality of lint produced by cotton genotypes of varying maturities are affected by different rates of soil applied K and N fertilization. Eight cotton genotypes representing a range of maturities and regional adaptations were studied in Mississippi in 1991 and 1992. All plots received a preplan! application of 112 kg ha−1 N and half the plots also received a 38 kg ha−1 sidedress application of N. Within each N treatment, half the plots received 112 kg ha−1 K surface applied and preplant incorporated, with the remaining plots receiving 0 kg ha−1 K. Averaged across years and N treatments, the K deficiency associated with the 0 K treatment reduced lint yield (9%), boll mass (7%), lint percentage (1%), and seed mass (4%). Varying the N fertilization did not benefit these parameters. The high N treatment reduced lint yield 3% (P = 0.07) and lint percentage 1% (P = 0.06) when coupled with the 0 K treatment. All genotypes suffered yield reductions caused by the K deficiency, except for ‘HS 26’, which was not adapted for production in the Mississippi Delta. Potassium deficiency produced reductions in fiber elongation (3%), 50% span length (1%), uniformity ratio (1%), micronaire (10%), fiber maturity (5%), and perimeter (1%) in all genotypes. Nitrogen application above the 112 kg ha− rate did not increase the lint yield under the growing conditions of our study. The data indicate that genotype was not of importance when dealing with K fertility. The deficiency itself, however, must be dealt with to avoid significant reductions in the yield and quality of fiber produced.

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 F(2.3) (HQ95-6x'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 F(2.3) (119- 5 sub-okrax'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).