Segregation distortion for seed testa color in Mungbean (Vigna radiata L. Wilcek).

Genetic segregation experiments with plant species are commonly used for understanding the inheritance of traits. A basic assumption in these experiments is that each gamete developed from megasporogenesis has an equal chance of fusing with a gamete developed from microsporogenesis, and every zygote formed has an equal chance of survival. If gametic and/or zygotic selection occurs whereby certain gametes or zygotic combinations have a reduced chance of survival, progeny distributions are skewed and are said to exhibit segregation distortion. In this study, inheritance data are presented for the trait seed testa color segregating in large populations (more than 200 individuals) derived from closely related mungbean (Vigna radiata L. Wilcek) taxa. Segregation ratios suggested complex inheritance, including dominant and recessive epistasis. However, this genetic model was rejected in favor of a single-gene model based on evidence of segregation distortion provided by molecular marker data. The segregation distortion occurred after each generation of self-pollination from F1 thru F7 resulting in F7 phenotypic frequencies of 151:56 instead of the expected 103.5:103.5. This study highlights the value of molecular markers for understanding the inheritance of a simply inherited trait influenced by segregation distortion.

Monitoring water pathways through mungbean pods using backscattered electron microscopy.

Weather damage by rainfall is a major constraint to production of high quality mungbean seed. Breeding mungbeans for weathering resistance is assisted by an understanding of the pod wall structure and how this structure can affect water absorption. This paper describes a simple microscopic technique for determining the transport route of salt solutions from the external pod surface through the pod wall tissues and into the pod lumen. Different mungbean cultivars were selected based on differences in field performance. Mungbean pods were immersed in concentrated salt solutions (lanthanum nitrate, caesium chloride and sodium chloride) for different time periods, embedded in resin blocks and polished prior to backscatter imaging in a field emission scanning electron microscope. The salts precipitated between the pod wall tissues and through timed experiments clearly demonstrated the passage of salt solution through the pod wall tissues and into the pod lumen. The sale molecules penetrated the outer epidermis and parenchyma but were unable to penetrate the dense sclerenchymatous layer beneath. The salt solution entered the lumen of the pod via the small gap between the suture cap and the dense tissue sheath. Although this technique may not provide a true determination of fresh water absorption through mungbean pods it does demonstrate a simple means of identifying more resistant pod structures suitable for use in achieving genetic improvement.