Jacob Mashilo

Genetic diversity of bottle gourd (Lagenaria siceraria (Molina) Standl.) landraces of South Africa assessed by morphological traits and simple sequence repeat markers

Bottle gourd (Lagenaria siceraria (Molina) Standl.) is an important crop in rural communities in South Africa but it remains under-researched. The objective of this study was to assess the genetic diversity present amongst bottle gourd landraces grown by smallholder farmers in South Africa using morphological traits and 11 selected polymorphic simple sequence repeat (SSR) markers. Marked phenotypic differences were observed amongst bottle gourd landraces. Principal component analysis on quantitative traits identified seven principal components, which accounted for 87% of the total variation. Number of alleles varied from 3 to 9 with a mean of 6 per SSR locus. Number of effective alleles ranged from 1.99 to 6.72 with a mean of 3.75. Shannons information index varied from 0.95 to 2.01 with a mean of 1.41. Expected heterozygosity values ranged from 0.5 to 0.87 with a mean of 0.71 with polymorphic information content values of 0.5 to 0.85 and a mean of 0.7. Morphological traits and SSR marker analyses showed a significant correlation in clustering the landraces. The present study demonstrated the presence of genetic diversity amongst bottle gourd landrace collections from South Africa useful for strategic improvement, direct production or conservation.

Yield-based selection indices for drought tolerance evaluation in selected bottle gourd [Lagenaria siceraria (Molina) Standl.] landraces

ABSTRACT Bottle gourd is an important crop in arid and semi-arid tropics where recurrent drought is the major constraint to crop production. Identification of drought-tolerant bottle gourd genotypes is fundamental to enhance productivity and for effective breeding and conservation. The objective of this study was to determine drought tolerance of a diverse set of bottle gourd landraces and to identify promising genotypes for direct production or breeding. A field study was conducted using a 12 × 2 factorial experiment involving 12 bottle gourd landraces under drought-stressed (DS) and non-stressed (NS) conditions. Significant differences were observed among bottle gourd landraces with respect to fruit yield under DS and NS conditions. The mean fruit yield under DS and NS conditions was 8.75 and 22.4 t ha−1, respectively. Drought stress reduced fruit yield by 62%. Correlation and principal component analyses revealed the significance of yield-based indices of drought tolerance, such as tolerance index, geometric mean productivity, stress tolerance, mean productivity, yield index and harmonic mean, which allowed discrimination of drought-tolerant bottle gourd landraces. Such landraces as BG-79, BG-31, BG-67, BG-52, BG-78 and GC were identified useful for drought tolerance breeding or rootstock development programs.

Correlation and path coefficient analyses of qualitative and quantitative traits in selected bottle gourd landraces

ABSTRACT Knowledge on associations between yield and related traits is vital to improve selection efficiency in cultivar improvement. This study determined the relationships among qualitative and quantitative traits in bottle gourd landraces using simple correlation and path analyses. Results showed significant and positive correlations between the number of fruits per plant (NFPP) with number of male flowers (NMF), number of female flowers (NFF), plant height (PHT) and number of branches (NB). Number of seeds per fruit (NSPF) positively correlated with PHT, NMF, NFF, NB and fruit weight (FW). Fruit texture, degree of warts (DW), fruit shape (FS), and degree of neck bending, stem-end fruit shape and fruit neck length (FNL) had significant negative correlations with NFPP or NSPF. Path analysis revealed high direct path coefficient value (0.96) between FW and NSPF. Also, positive direct path coefficient value (0.92) was exhibited between NFF and NFPP. Relatively high direct path coefficient value (0.47) was exhibited between DW and NSPF. This study demonstrated that selection for increased FW and NFF may improve genetic gain in seed yield and fruit yield in bottle gourd breeding. Using the above analyses, the following landraces such as BG-06, BG-07, BG-09, BG-11, BG-13, BG-24 and BG-67 were selected for breeding.

Genetic differentiation among selected tepary bean collections revealed by morphological traits and simple sequence repeat markers

ABSTRACT Understanding the genetic relationship of crop ideotypes is essential for genetic analysis and breeding. The objective of this study was to determine genetic differentiation present among 20 selected tepary bean (Phaseolus acutifolius A. Gray) genotypes using morphological traits and simple sequence repeat (SSR) markers in order to identify genetically unique parental lines to develop breeding populations. Phenotypic diversity was estimated using Shannon-Weaver diversity index (H’), principal component analysis (PCA) and cluster analysis (CA). Genotypic diversity was estimated using Jaccards genetic distances and CA. Shannon-Weaver diversity index values for the studied morphological traits ranged from 0.89 to 0.99, with a mean of 0.95 revealing high phenotypic differences among test genotypes. PCA identified four useful principal components (PCs) which contributed to 73% of the total phenotypic variation of collections. PC1 accounted for 28% of the total variation correlated to dry shoot mass and number of pods per plant. PC2 correlated with number of seeds per pod, grain yield and harvest index and contributed to 21% of total variation. The mean observed (Ho) and expected (He) heterozygosity values were 0.45 and 0.51, respectively revealing moderate genetic differentiation among genotypes. The mean polymorphic information content was 0.52, suggesting efficient discriminatory power of the SSR loci useful in future tepary bean genetic diversity analysis. The current study revealed moderate genetic differentiation among the studied tepary bean genotypes. Morphological traits and SSR markers well-correlated in allocating the tepary bean genotypes. The following genotypes were genetically distinct: G40201, G40237, G40068, G40033 and G40063 which are recommended for further crosses, selection and population development.

Variance components and heritability of yield and yield-related traits in tepary bean (Phaseolus acutifolius)

The extent of variance and heritability of traits influence the response to selection in crop breeding programs. The objective of this study was to determine variance components and heritability in tepary bean (Phaseolus acutifolius A.Gray) populations to identify promising genotypes for strategic breeding or direct production. Fifty genetically diverse tepary bean genotypes were evaluated under two contrasting environments using a 5 × 10 alpha lattice design with two replications. Results showed significant (p ≤ 0.05) differences among genotypes (G), environment (E) and G × E interaction for most of the studied traits. Phenotypic coefficient of variation values were higher than genotypic coefficient of variation for the studied traits, indicating greater contribution of genetic and environmental components influencing phenotypic variation. High broad-sense heritability and genetic advance were observed for grain yield (GY) and harvest index (HI), indicating better selection response for these traits in the population. Path coefficient analysis indicated that direct selection for HI could increase genetic gains for GY in tepary bean. Genotypes G40020, G40023, G40084, G40135, G40139, G40140, G40144A, G40145, G40157, G40159, G40173A, G40237 and G40284 exhibited better yield and yield components and were selected for breeding or population development in tepary bean.

Leaf gas exchange and water-use efficiency of dry-land wheat genotypes under water stressed and non-stressed conditions

ABSTRACT The objective of this study was to determine drought tolerance characteristics of dryland wheat genotypes based on leaf gas exchange and water-use efficiency in order to identify promising genotypes for drought tolerance breeding. Physiological responses of ten genetically diverse wheat genotypes were studied under non-stressed (NS) and water stressed (WS) conditions using a 2 × 10 factorial experiment replicated 3 times. A highly significant water condition × genotype interaction (P < 0.001) was observed for photosynthetic rate (A), ratio of photosynthetic rate and internal CO2 concentration (A/Ci), ratio of internal and atmospheric CO2 (Ci/Ca), intrinsic (WUEi) and instantaneous (WUEinst) water-use efficiencies suggesting genotypic variability among wheat genotypes under both test conditions. Principal component analysis (PCA) identified three principal components (PC’s) under both test conditions accounting for 84% and 89% of total variation, respectively. Bi-plot analysis identified G339 and G344 as drought tolerant genotypes with higher values of A, T, gs, A/Ci, WUEi and WUEinst under WS condition. The current study detected significant genetic variation for drought tolerance among the tested wheat genotypes using physiological parameters. Genotypes G339 and G344 were identified to be drought tolerant with efficient A, T, gs, A/Ci and water-use under water stressed condition.