Cytogenetics of Brassica juncea×Brassica rapa hybrids and patterns of variation in the hybrid derivatives

Abstract

Interspecific hybridization is an important tool to elucidate intergenomic relationships, transfer characters across species and develop synthetic amphidiploids, and it has been widely applied for improving brassicas. The objective of the present study was to create genetic variability in Brassica through interspecific hybridization. Crosses between Brassica juncea (AABB, 2n ¼ 36), and Brassica rapa (AA, 2n ¼ 20) vars toria, yellow sarson, and brown sarson were attempted, and the hybrid derivatives were advanced to the F 4 generation. Hybrids were obtained from the crosses B. juncea · toria and B. juncea · yellow sarson. The F 1 plants were vigorous and intermediate to the parents in many morphological traits. The meiotic study of AAB hybrids showed 10 II + 8 I in the majority (71.8%) of cells analysed. A maximum of 12 and a minimum of seven bivalents were also observed in a few cells. The occurrence of multivalent associations (trivalents to pentavalents) at diakinesis/metaphase I and a bridgefragment configuration at anaphase I were attributed to homoeology between A and B genomes. A high percentage of plants resembling B. juncea was observed in the F 2 generation. Transgressive segregation in both directions was found for plant height, primary branches, main raceme length, siliquae on main raceme, siliqua intensity, seeds per siliqua and seed yield. There were significant differences for the 14 characters in the F 4 derivatives. Moderate to high estimates of phenotypic and genotypic coefficients of variation, broad-sense heritability, and expected genetic advance were found for seed yield, 1000-seed weight, siliquae per plant, seeds per siliqua and days to flowering. Intergenomic recombination, reflected as wide variation in the hybrid progenies, permitted the selection of some useful derivatives.

Cytomorphology of Brassica napus × B. rapa hybrids and patterns of variation in the F2 derivatives

“…Choudhary et al (2002) also reported a high frequency of the maternal and intermediate types of plants in F 2 generation of B. juncea  B. rapa crosses. Wide phenotypic variation and transgressive segregation for plant height, primary branches per plant, main raceme length, siliquae on main raceme and seed yield per plant in the F 2 generation might have resulted from recombination and or eventual segregation of aneuploid forms arising in the populations.…”

“…Prakash (1973) succeeded in obtaining some high-yielding physiological variants from segregants of the B. campestris  B. nigra cross. Similarly, Rao et al (1993) and Choudhary et al (2002) obtained transgressive segregants for yield components from the F 2 generation of B. napus  B. carinata and B. juncea  B. rapa crosses, respectively. Thus present study indicated that interspecific hybridization in Brassica could be a valuable source for generating variability.…”

“…Such crosses generate genetic variation (Prakash 1973;Choudhary et al 2002), genetic diversity (Choudhary and Joshi 2001) and are also useful to transfer valuable characters across the species (Prakash and Chopra 1988;Sharma and Singh 1992). Various species of Brassica are grown in different parts of the world depending on their local importance and specific adaptability.…”

Cytomorphology of <i>Brassica juncea </i>× <i>B. napus</i> Hybrids and Pattern of Variation in the F₂ Derivatives

“…Olsson (1960aOlsson ( , 1960b) also found wide variation in plant height, flowering and maturity, siliqua size, and pollen fertility in F 2 and F 3 plants of the cross B. rapa B. nigra. Similarly, Rao et al (1993) and Choudhary et al (2002) obtained transgressive segregants for yield components from the F 2 generation of B. napus B. carinata and B. juncea B. rapa crosses, respectively. Non-homologous pairing and the resultant exchange between chromosomes of different genomes would play an important role for creating a wide range of variability (Prakash 1973b), and thus provide immense opportunity for broadening the gene pool in the genus Brassica.…”

The use of cytogenetic tools for studies in the crop-to-wild gene transfer scenario

“…The simplest method to evaluate male fertility is pollen staining with traditional stains like aceto-carmine and acid fuchsin (e.g., Choudhary et al, 2002;Chen et al, 2003;Matsuoka et al, 2007). This allows a rapid confirmation of pol-len sterility, often accompanied with indehiscence of anthers in totally sterile hybrids.…”