**9. Mapping of genes/QTLs**

Increasing the seed weight has been one of the major objectives to develop high yielding varieties. Molecular markers are now available which are linked to orthologous seed weight loci. RFLP markers to locate major QTLs for orthologous seed weight in mungbean. They found that the genomic regions in cowpea and


**57**

*Mungbean (*Vigna radiata *L. Wilczek): Retrospect and Prospects*

mungbean that have the major effect on seed weight span the same RFLP markers in both the species. These markers are co-linear in arrangement on homologous linkage groups in both the crops. Attempts to breed large and hard seeded varieties of mungbean have not been very successful because of negative genetic correlation between these two traits as a result of pleiotropy or genetic linkage. Studies on the genetic relationship between hard seededness and seed weight, however, are not conclusive. QTL mapping approach using molecular markers have been employed

In order to develop high yielding disease resistant varieties in mungbean, the common breeding methods employed were pure line selection, hybridization followed by pedigree selection, mutation breeding and wide hybridization. While exercising selection, major emphasis has been placed on short duration, photo and thermo-insensitivity, synchronous maturity and resistance to mungbean yellow mosaic virus and powdery mildew. More than 150 varieties have been developed in India employing pure line selection, pedigree method of selection following hybridization, mutation and wide hybridization. The first variety of mungbean was Type 1 developed from local selection of Muzaffarpur (Bihar), which has been extensively been used afterward as one of the parents in hybridization programmes for the development of improved varieties like Type 2, K 851, T 44 and Sunaina. Utilization of T 44 in hybridization has resulted in the development of Pusa Baisakhi which, in turn, has given PIMS 4 and Jyoti. Through mutation breeding, about 14 varieties using gamma rays or occasionally ethyl methane sulphonate as mutagens have been developed. Varieties developed through mutation like CO 4, Pant Moong 2, TAP 7,

The main reason that the expected yield advances by the conventional component breeding methods have not materialized in mungbean is that the parents used in crossing programmes are not duly evaluated before their use. Seed yield of parents has a positive significant bearing on the yield of the progenies and in the inheritance of this character, additive variance is of paramount importance than the nonadditive variance, although many a times the latter also has significant bearing. The choice of the parents besides on their agronomic attributes like yield and its components must also be based on their genetic diversity, phenotypic stability and combining ability. So logically all the would-be parents must be evaluated by their progeny tests across environments and locations before their use in a crossing programme. A progeny test provides genetic composition of the parental plants and helps in selection of superior ones. In self-pollinated crops like mungbean, many minor genes of additive effect control yield and in any breeding programme, the ultimate goal is to accumulate and harness these genes. High yielding varieties from different genetic backgrounds and carrying different genes for yield when crossed and subjected to replicated progeny tests are expected to generate higher frequency of high yielding plants. Yield stability in mungbean is very important owing to significantly variable response of high yielding varieties across locations and years. Work on stability analysis done in mungbean shows that no high yielding varieties are stable across time and space. All the potential parents in a hybridization programme must be evaluated for their mean yield performance and yield stability, F1 performance, F2 mean yield and the variance generated,

to investigate the linkage relationship between these two traits (**Table 2**).

*DOI: http://dx.doi.org/10.5772/intechopen.85657*

**10. Breeding approach**

BM 4, MUM 2 and TARM 1.

**10.1 Parental selection**

#### **Table 2.** *Genes/QTLs/remarks of important traits.*

*Mungbean (*Vigna radiata *L. Wilczek): Retrospect and Prospects DOI: http://dx.doi.org/10.5772/intechopen.85657*

mungbean that have the major effect on seed weight span the same RFLP markers in both the species. These markers are co-linear in arrangement on homologous linkage groups in both the crops. Attempts to breed large and hard seeded varieties of mungbean have not been very successful because of negative genetic correlation between these two traits as a result of pleiotropy or genetic linkage. Studies on the genetic relationship between hard seededness and seed weight, however, are not conclusive. QTL mapping approach using molecular markers have been employed to investigate the linkage relationship between these two traits (**Table 2**).

#### **10. Breeding approach**

*Legume Crops – Characterization and Breeding for Improved Food Security*

characters and broaden the genetic base.

**8. Molecular diversity analysis**

in mungbean germplasm.

**9. Mapping of genes/QTLs**

*Genes/QTLs/remarks of important traits.*

65–70 days for spring season combining determinate growth habit, high harvest index and reduced photoperiod sensitivity are required. For summer cultivation, extra early varieties of 55–60 days with synchronous maturity are desirable. Vegetative growth should terminate with flowering and assimilates should be transported to developing pods [65, 66]. Recently, large seeded varieties like Pusa Vishal, SML 668, TMV 37, etc., with early and synchronous maturity have been developed which have great market demand. To break the yield plateau in mungbean, there is a need to develop suitable plant type for target environments. In high input cerealcereal systems, mungbean has to fit in gaps. For this, plant type that is determinate, photo-thermo insensitive, early maturing and high yielding with high harvest index needs to be developed. Good seedling vigour, distinctive vegetative and reproductive phases and high harvest index will be essential components of this plant type. There is good scope to utilize wild and cultivated *Vigna* species to incorporate novel

Assessment of genetic diversity using RAPD analysis shows close similarity among mungbean cultivars [67]. The study reveals narrow genetic base of Indian cultivars probably due the repeated use of limited ancestors in their pedigrees. This observation has further been confirmed using RAPD [68, 69] and ISSR [70, 71] markers. Amplified fragment length polymorphism (AFLP) markers have also been used in mungbean to test their usefulness in genetic diversity assessment [67]. The long primers yielded significantly higher number of discrete and detectable bands as well as polymorphic bands than 10-base primers. The results show that long primers can be used efficiently for analyzing genetic diversity and the relationships

Increasing the seed weight has been one of the major objectives to develop high yielding varieties. Molecular markers are now available which are linked to orthologous seed weight loci. RFLP markers to locate major QTLs for orthologous seed weight in mungbean. They found that the genomic regions in cowpea and

**Characteristic Marker Genes/QTLs/remarks References** Seed weight RFLP Major QTLs [72] RFLP Suggested a weak association between seed weight

population

Powdery mildew RFLP Genes, '13 m' and 'Thiz2' identified in a cross VC3890 × TC1966

in mungbean

and hard seededness in mungbean by analyzing a F2

RFLP Four loci for hard seededness and 11 loci [63]

RFLP Two QTLs, '13MR1' and 'PMR2' have been identified [73]

variation associated with resistance to powdery mildew

RFLP A single locus has been identified that explains 86% of

[62]

[65]

[74]

**56**

**Table 2.**

In order to develop high yielding disease resistant varieties in mungbean, the common breeding methods employed were pure line selection, hybridization followed by pedigree selection, mutation breeding and wide hybridization. While exercising selection, major emphasis has been placed on short duration, photo and thermo-insensitivity, synchronous maturity and resistance to mungbean yellow mosaic virus and powdery mildew. More than 150 varieties have been developed in India employing pure line selection, pedigree method of selection following hybridization, mutation and wide hybridization. The first variety of mungbean was Type 1 developed from local selection of Muzaffarpur (Bihar), which has been extensively been used afterward as one of the parents in hybridization programmes for the development of improved varieties like Type 2, K 851, T 44 and Sunaina. Utilization of T 44 in hybridization has resulted in the development of Pusa Baisakhi which, in turn, has given PIMS 4 and Jyoti. Through mutation breeding, about 14 varieties using gamma rays or occasionally ethyl methane sulphonate as mutagens have been developed. Varieties developed through mutation like CO 4, Pant Moong 2, TAP 7, BM 4, MUM 2 and TARM 1.

#### **10.1 Parental selection**

The main reason that the expected yield advances by the conventional component breeding methods have not materialized in mungbean is that the parents used in crossing programmes are not duly evaluated before their use. Seed yield of parents has a positive significant bearing on the yield of the progenies and in the inheritance of this character, additive variance is of paramount importance than the nonadditive variance, although many a times the latter also has significant bearing. The choice of the parents besides on their agronomic attributes like yield and its components must also be based on their genetic diversity, phenotypic stability and combining ability. So logically all the would-be parents must be evaluated by their progeny tests across environments and locations before their use in a crossing programme. A progeny test provides genetic composition of the parental plants and helps in selection of superior ones. In self-pollinated crops like mungbean, many minor genes of additive effect control yield and in any breeding programme, the ultimate goal is to accumulate and harness these genes. High yielding varieties from different genetic backgrounds and carrying different genes for yield when crossed and subjected to replicated progeny tests are expected to generate higher frequency of high yielding plants. Yield stability in mungbean is very important owing to significantly variable response of high yielding varieties across locations and years. Work on stability analysis done in mungbean shows that no high yielding varieties are stable across time and space. All the potential parents in a hybridization programme must be evaluated for their mean yield performance and yield stability, F1 performance, F2 mean yield and the variance generated,

combining ability and their interaction with the important environmental variables. All these variables give a measure of the comparative potential of different F2 crosses. It is desirable that the progenies of only those parents be advanced beyond F2 generation that show high grain yield, yield stability, a positive general combining ability for grain yield and that are of distant genetic origin. Progenies of parents with low yield and negative general combining ability for yield must not be advanced beyond F2 generation. In an intra-species crossing programme, one parent should be a good agronomic base with higher stability and the other parent a good general combiner for yield and its components. Crosses with this strategic selection of parents are expected to give a wide range of genetic variability. To achieve stability and get a true measure of inherent genetic potential, the parental lines must be tested over a number of locations and get their combining ability estimates.

#### **10.2 Component breeding**

Fifty years of conventional approach of engineering different yield components in mungbean to build up a new plant type with higher productivity levels has thus far given only modest yield gains over the traditional cultivars. This approach has failed to break the present yield barriers as a whole and bring changes of scale. Based upon correlation analysis of various yield components, selections have been based mainly on number of pods per plant, seeds per pod and 100-seed weight and sometimes also on number of pods per bunch and branches per plant or podding per unit area usually called 'Pod Index'. Pods per plant is by far the most important yield component and almost all the workers have found it having positive correlation with seed yield. It is the best selection index for seed yield and could be increased by increasing number of branches per plant or number of bunches per plant or by increasing the number of pods per bunch. Most of the work has shown that branch number per plant is negatively correlated with seed yield, but bunches per plant has mostly been found to be positively correlated with seed yield. Ramanujam [75] and others have found that pods per bunch and bunches per plant both are positively correlated with yield. Increasing pods per bunch is physiologically constrained in grain legumes owing to fall of flowers and unripe or partially filled pods. It seems the most feasible path to increase seed yield is through increasing number of bunches per plant. This in essence means a plant with more number of nodes with a shorter internode length, with three to four erect branches emerging from the lower to lower-middle nodes at around 20–30° angle with the main stem, and sympodial bearing of pod inflorescences coming from the upper nodes of the main stern, each carrying around 8–10 pods. Number of seeds per pod has been shown mostly positively correlated with seed yield but many workers show it to be negatively correlated with yield. However, an optimal level of 14–16 seeds per pod should be a breeders objective. Seed weight is generally negatively correlated with seed yield but some results have shown it to be positively correlated. The strength of the newly developed second generation varieties like Pusa Vishal and Pusa Ratna lies in the fact that they have more seeds per pod (12–16) with higher 100-seed weight (5.0–5.5 g) without compromising on the pod number per plant. Many researchers advocated cereal mimics with sympodial bearing and suggested increasing pods per plant through the path of increasing the average number of pods per node and building up a soybean like plant type in mungbean [76]. He found the main stem bearing under the control of a single recessive gene and normal conventional bearing to the incompletely dominant. Plant height has been found positively

**59**

*Mungbean (*Vigna radiata *L. Wilczek): Retrospect and Prospects*

correlated with seed yield. An optimal upright plant height incorporates more functional nodes and thus more number of pods per plant. After pods per plant, this is the second most important character to be used for selection of seed yield. Owing to their high heritability, 100-seed weight and branch number could be excellent selection criteria but for their unfavorable correlations with yield. Also due to the compensatory mechanisms operating within the plant as a whole, this correlation based selection methodology has not brought the desired productivity levels in mungbean. Alternatively, the best option is direct selection for seed yield

Most of the high yielding varieties of mungbean bred and released so far have been developed through single cross pedigree method of selection. The single plant selections made in the early generations restrict carrying forward the bulk of created variability, which gets lost quickly giving way to homozygosity with each succeeding generation. This method has served the mungbean improvement programme well in the past, but lately no productivity advances are materializing due to the inherent genetic limitation of the method. The intermitting of selected F2 plants and selections in the late generations will help to harness most of the desir-

The early generation yield trials allow early identification of better performing crosses and F, derived lines within the individual crosses. However, selection emphasis is given in later generations only. The F2 derived family selection is very appropriate in mungbean, which is prone to high GE interactions and low seed increase ratio, which renders pedigree, bulk and single seed decent methods inefficient. The time required is less and emphasis is on grain yield in replicated progeny tests. It was developed in Canada as a modification of bulk method. The F2 derived family selection takes benefits of early generation yield testing to eliminate efficiently all the undesired materials both between and within the hybrid populations. Replicated yield trials are conducted across locations/environments for early generation selections among and within populations. These selections are further evaluated and final selections for high yield are made in only the best of families or populations. Due emphasis must be given to make site specific selections for different agro-climatic and production systems. Also depending upon the demands of the location and system, input responsiveness of the selections under high management

Both physical and chemical mutagens have been employed in improvement of mungbean crop India. The main drawbacks of this method are that the frequencies of desirable mutants are very less, necessitating evaluation of very large population and the difficulty in identification and scoring of micromutations. Tickoo and Chandra [77] using both physical and chemical mutagens could induce significantly higher variability in mungbean for characters like yield per plant, pods per plant, seed number per pod, seed weight, days to flower and harvest index in M2, generation. Mean values of all the characters had a negative shift in M2 but after selection changed to positive direction in M3 but were still associated with significantly

*DOI: http://dx.doi.org/10.5772/intechopen.85657*

**10.3 Conventional breeding methods**

on a unit area basis.

able genes.

**10.4 Early generation testing**

conditions may be tested.

**10.5 Mutation breeding**

correlated with seed yield. An optimal upright plant height incorporates more functional nodes and thus more number of pods per plant. After pods per plant, this is the second most important character to be used for selection of seed yield. Owing to their high heritability, 100-seed weight and branch number could be excellent selection criteria but for their unfavorable correlations with yield. Also due to the compensatory mechanisms operating within the plant as a whole, this correlation based selection methodology has not brought the desired productivity levels in mungbean. Alternatively, the best option is direct selection for seed yield on a unit area basis.
