Evaluation of guar (Cyamopsis tetragonoloba (L.) Taub.) for gum and agronomic trait quality
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Traditional breeding improvement of guar (Cyamopsis tetragonoloba (L.) Taub.) depends heavily on the understanding of their inheritance mechanism. Reciprocal crosses of two lines of guar, namely PI 217923 and ‘Lewis’, which exhibited disparate gum content (fg%) and branching habit, were done and progeny populations formed to study the heritability of gum content (fg%) and basal branching. Five F1 plants of ‘Lewis’ × PI 217923 and two F1 plants of PI 217923 × ‘Lewis’ were obtained by hand pollination. F1 plants of PI 217923 × ‘Lewis’ and ‘Lewis’ × PI 217923 exhibited branching habit of PI 217923. All seven F1 hybrids were self- pollinated to form F2 populations. Fg% of four plant introductions (PI) and four commercial varieties were compared in Lubbock in four years. Estimates of broad-sense heritability (h2B) of fg% in ‘Lewis’ × PI 217923 and PI 217923 × ‘Lewis’ were 75.53% and 52.74%, respectively. Estimates of narrow-sense heritability (h2N) of fg% were 40% and 29% for ‘Lewis’ × PI 217923 and PI 217923 × ‘Lewis’, respectively. At least one pair of genes was estimated to control the fg% expression in these two crosses. Significant differences of fg% were found among these eight accessions. PI 217923 was found to have the highest fg% among the eight accessions. χ2 goodness- of- fit test revealed that two of five F2 populations of ‘Lewis’ × PI 217923 and one of the two F2 populations of PI 217923 × ‘Lewis’ had a good fit of 3: 1 ratio under field grown conditions. When grown under greenhouse conditions with wider spacing, branching types of F2 populations of ‘Lewis’ × PI 217923 and PI 217923 × ‘Lewis’ segregated in a 3: 1 ratio, indicating that basal branching is controlled by one dominant gene. The gene symbol Brh-1 is proposed for this locus Black seeds of guar are believed to have of low quality. In the present experiment, seeds with different seed coat colors were studied to examine the effect of seed coat color on the hydration rate, germination, quantity of seed component, and gum content (fg%). Seeds of PI 217923, PI 340246, and ‘Lewis’ were studied. Seed coat blackening was found to affect the water absorption rate during guar seed germination. Hydration rate of dark grey and black colored seeds was significantly higher than that of light colored seeds. An interaction between genotype and seed coat color on seed germination was detected. Overall, seeds of darker color have significantly higher germination rate than that of light colored seeds across varieties. The quantity of endosperm (%) of black (42.7%) and dark grey (42.6%) colored seeds were significantly higher than that of light colored seeds (40.1%), with no difference between dark grey and black colored seeds. Significant differences of seedcoat quantity (%) were observed among these three different colored seeds with order from high to low: light (16.2%), dark grey (13.8%), and black (12.9%). Gum content (%) as determined by viscosity was not affected by seed coat blackening. Higher hydration rate and germination rate in dark grey and black colored seeds are possibly caused by seed coat degeneration or damage after maturation. Morphological and RAPD (random amplified polymorphic DNA) markers of eight accessions including four commercial varieties and two plant introductions (PIs) of Cyamopsis tetragonoloba (L.) Taub., one C. senegalensis Guill. and Perr., and one C. serrata Schinz. were used to study the genetic variation among Cyamopsis species. RAPD analysis showed that polymorphic bands detected by each primer across the eight accessions ranged from seven to 20 with a mean of 12.4, while the polymorphism level of band detected by the eight primers ranged from 46.7% (OG06) to 100% (F10, OE01, OC07, F04, and OA17) with a mean of 85.4%. Total bands of 12 to 15 detected for each accession by these eight primers were observed. Mean of bands detected by each of the eight primers for each accession ranged from 1.5 to 1.9. These eight accessions were grouped into three different groups at the average distance of about 1.2. Cluster analysis of nine morphological characters showed same result as using DNA markers but with more variation detected. Among the three species, C. serrata and C. senegalensis were grouped into one group, while those entries belonged to C. tetragonoloba grouped into another one.