Efrem Bechere

Stability of performance of tetraploid wheat landraces in the Ethiopian highland

Plant breeding has always been concerned with genotype-environment interaction. Normally high and stable performance are desirable attributes of cultivars. However, this is practically difficult to achieve where environmental variations are high and unpredictable and significant genotype-environment interactions occur. Stability of performance of 13 landraces evaluated at 4 different locations for 3 years in the highlands of Ethiopia was investigated. The testing locations have different climatic and edaphic conditions providing the conditions necessary for the assessment of stability. Stability parameters like b, s2d, s2, r2 and cv which are in common use were employed. Grain yield and 1000-kernel weight were the agronomic traits considered for the stability analysis. There were differences in the ranks of genotypes across the locations. Significant main environmental as well as interaction effects were observed showing the importance of genotype-environment interaction in both traits. Many of the landraces evaluated are rated as stable for these traits within the environmental conditions prevailing in these highland locations. Genotypes with specific adaptation to poor and favourable conditions were also identified. Certain genotypes showed similar manners of adaptation and stability for both of the traits. Grain yield showed low correlations with the stability parameters showing the possibility of attaining high yield and stability. Correlations between the stability parameters were mainly positive and significant for grain yield. Only a few of these correlations were found to be significant for kernel weight. The good adaptability of landraces should be exploited in the improvement of their yield potential.

Development of ‘naked-tufted’ seed coat mutants for potential use in cotton production

Use of chemical mutagenesis has been highly successful in most major crops. The objective of this research was to develop ‘naked-tufted’ seed mutants and to incorporate this genetic trait into cotton to enhance crop quality and reduce processing costs. In 1997, six commercial cultivars were treated with 2.45% v/v ethyl methane sulfonate. In 1999, three M3 plants were identified that had partially naked seed coats. The trait was stabilized through individual plant selections from 2000 to 2004. During 2005 and 2006, the homozygous naked-tufted M8 mutant lines were evaluated for lint yield, lint percent, fibers/seed, fibers/mm2, fiber quality, seed oil content, ginning efficiency and yarn spinning performance. Overall, the naked-tufted seed mutants had lower lint yield, lower fibers/seed, lower lint/seed, and lower fibers/mm2 when compared with their original fuzzy parents. The lint turnout from the mutants was similar to the fuzzy parents and the commercial cultivars. The naked-tufted seed mutants had higher seed oil percent, 6–17% lower short fiber contents, significantly reduced seed coat neps (37–42%), higher elongation and yarn tenacity than their fuzzy counterparts. Preliminary data also showed that the naked-tufted mutants required less energy to gin.

Mutagenesis Systems for Genetic Analysis of Gossypium

The recent evolution of tetraploid cotton combined with intensive selection of cultivated cottons has reduced the genetic diversity of cotton. This lack of allelic diversity hampers efforts to improve the agronomic traits of cotton and limits the application of molecular genetic tools for improvement of cotton germplasm. The lack of genetic resources also reduces our ability to understand the molecular mechanisms that regulate cotton growth and development and its responses to environmental stresses and pathogens. Use of a variety of chemical mutagens and ionizing radiation can be used to effectively increase the frequency of mutant alleles in Gossypium species. While application of insertional mutagenesis methodologies that require high-throughput plant transformation procedures is not feasible, evaluation of various transposon-based mutagenesis systems is underway. TILLING technology, which uses a combination of mutagenesis and high-throughput molecular screening methods for reverse genetics is also being developed.

Genome-wide analysis of gene expression of EMS-induced short fiber mutant Ligon lintless-y (liy) in cotton (Gossypium hirsutum L.)

In this work we describe a chemically-induced short fiber mutant cotton line, Ligon-lintless-y (liy), which is controlled by a single recessive locus and affects multiple traits, including height of the plant, and length and maturity of fiber. An RNAseq analysis was used to evaluate global transcriptional changes during cotton fiber development at 3, 8 and 16days post anthesis. We found that 613, 2629 and 3397 genes were significantly down-regulated, while 2700, 477 and 3260 were significantly up-regulated in liy at 3, 8 and 16 DPA. Gene set enrichment analysis revealed that many metabolic pathways, including carbohydrate, cell wall, hormone metabolism and transport were substantially altered in liy developing fibers. We discuss perturbed expression of genes involved in signal transduction and biosynthesis of phytohormones, such as auxin, abscisic acid, gibberellin and ethylene. The results of this study provide new insights into transcriptional regulation of cotton fiber development.

Quantitative trait loci analysis for net ginning energy requirements in upland cotton (Gossypium hirsutum L.)

Cotton cultivars with reduced fiber-seed attachment force have the potential to be ginned faster with less energy. The objective of this study was to identify quantitative trait loci (QTL) for net ginning energy requirement (NGE), and its relationship with other fiber quality traits in upland cotton. Two cotton lines, TAM 182-34 ELS and AR 9317-26, with significant differences in NGE and fiber-seed attachment force, were crossed and 285 F2 plants derived from a single F1 plant were planted in the field and leaf samples collected for DNA marker analysis (Population A). Individual F3 plants and the two parents were planted in replicated progeny rows. The cotton was ginned on a 10-saw laboratory gin stand. Electrical power used by the gin was measured and recorded with a Yokogawa CW121 power meter. Fiber quality attributes were measured using a high volume instrument. A total of 455 SSR marker loci were used to construct a linkage map. Two QTLs were identified for NGE on chromosomes 12 and 20, associated with markers CIR148 and DPL0600, explaining 14 and 8.8% of the phenotypic variation, respectively. NGE shared the same genomic region with fuzz percent on chromosome 12. Population B, consisting of 260 F2 progeny from the reciprocal cross AR 9317-26 X TAM 182-34 ELS, was used to confirm these QTLs by analyzing SSR markers mapped on Chrs 12 and 20. These QTLs (qNGE-c12 and qNGE-c20) were confirmed and appeared stable. Further validation of significantly associated markers on different populations is necessary prior to implementation in marker-assisted selection.

Differences among Cotton Genotypes for Fiber-Seed Attachment Force

Cotton fibers are more loosely attached to seed for some genotypes, and genotypes with reduced fiber-seed attachment force have the potential to be ginned faster with less energy and less fiber damage. The objective of this paper was to evaluate 15 genotypes to determine how net gin stand energy usage (that above idling), ginning rate, and fiber quality relate to fiber-seed attachment force. Attachment force was measured with a pendulum-type tester for tufts of fiber on each side of the seed oriented towards the chalazel (rounded) end of the seed, micropyle (pointed) end of the seed, or in between (middle); and two sample preparation techniques were evaluated. Genotypes exhibited a wide range of net gin stand energy (7.5 to 12.0 Wh/kg lint) and ginning rate (2.5 to 3.3 g lint/sec) when ginned on a 10-saw laboratory gin stand, and overall fiber-seed attachment force range from 36.1 to 64.1 cN*cm/mg fiber. There was a strong correlation (r = 0.87) between net gin stand energy and fiber-seed attachment force, but only a slight correlation (r = -0.38) between ginning rate and fiber-seed attachment force. Increased fiber-seed attachment force and increased fiber length both together increased net gin stand energy, though fiber-seed attachment force was the dominant component of the relationship. Increased seed coat nep counts were observed with either increased fiber-seed attachment force (r=0.72) or increased net gin stand energy (r=0.82). The results of this study validated the assumption that net gin stand energy measurements can be used to predict genotype differences in fiber-seed attachment force, but it may be important to consider the effects of fiber length. These findings are important as net gin stand energy can be determined much more quickly than fiber-seed attachment force and may be used as an effective breeding tool.