Exploration, Collection and Characterization of Horsegram [Macrotyloma uniflorum (Lam.) Verd.] Germplasm

Horsegram [Macrotyloma uniflorum (Lam) verd.] is an underutilized arid food legume known to grow well in diverse environmental conditions like poor soils, low rainfall etc. Horsegram grows in a soil pH of 5.0 to 7.5 and at an altitude of 1800 range (Sunil et al., 2009). Horsegram is the fifth most important widely grown pulse crop species grown in India (Fuller 2018) indicating its wide spread and importance since the Neolithic period. Horsegram is also known as madras bean or poor man pulse. Archeological investigations have revealed that use of horsegram as food in India dates back to 2000 B.C (Mehra 2000). Horsegram is used for fodder, feed, seed, green manuring and in ayurvedic medicine. Horsegram is leguminous self-pollinated, drought tolerant rabi crop, generally used as cattle feed in Andhra Pradesh. 
       
Globally, efforts in conservation of germplasm of horsegram is poor compared to other pulse crops.  A total of 1721 accessions of horsegram are being conserved in different gene banks of the world (Chahota 2013) of these 95% are conserved at NBPGR; New Delhi. Horsegram is native to India (Bogdan 1977). The Eastern Ghats of Andhra Pradesh i.e., Araku region is a rich source of diversified germplasm of legumes, medicinal plants, millets and ancient crops. Among which, horsegram is one of the crop with wide diversified germplasm. The tribals play a major role in conservation of the germplasm right from their ancestors.  Mostly, they cultivate the ancestral local varieties. Broadening the genetic base in horsegram through interspecific hybridization employing diverse germplasm will be useful in improving pest and disease resistance, grain quality, protein percentage and also reducing nutritional factors (Dikshit 2014).

Exploration and collection
 
Exploration and collection of horsegram germplasm was carried out during Rabi 2018 in Tribal tracts and Eastern Ghats of Andhra Pradesh (Araku region) in India. Araku hill station is located in Visakhapatnam district of Andhra Pradesh in the Eastern ghats at 18.333^oN and 82.866^oE, altitude of 1300 m from Mean Sea level. The tribals residing in the regions are majorly belong to Bhagatas, Kondadoras, Kondulu, Valmikas, Kotiya, Kondakumaras and Bondalu tribes. The soil type of the region is red and sandy loams. Temperatures range from 8^oC to 37^oC with an annual rainfall of 1700 mm. A total of 25 germplasm lines were collected using GPS co-oridnates using Garmin etrex 30x hand held GPS machine. Random and bulk sampling methods were adopted for collecting the germplasm data. Passport data of each accession line was collected as per the standard procedures provided by ICAR-NBPGR, New Delhi (Pareek et al., 2000). The horsegram germplasm lines were collected from the farm fields, threshing floors and house hold stores of the farmers by scientist of Agricultural Research Station Yellamanchili, with the aid of local Agricultural departmental officials during Rabi 2018.
 
Morphological characterization
 
The 25 germplasm lines collected were evaluated during Rabi 2019 at Agricultural Research Station, Yellamanchili, Visakhapatnam (DT.) Andhra Pradesh. The germplasm lines were laid out in randomized block design with two replications in a plot of size of 3.6 m² and spacing of 30 × 15 cm. Each entry was sown in three rows. The statistical analysis was carried out for the biometrical parameters. Germplasm lines were morphologically characterized and observations were recorded from five randomly selected plants in each genotype, for, plant height (cm), no. of branches per plant; no. of pods per plant, 100 seed weight (g), dry haulm weight (g) per plant, number of seeds per pods, leaf colour, flower colour, stem hairiness, twining habit and seed yield per plant (g). Days to 50% flowering; days to maturity, leaf hairiness and seed coat colour were recorded on plot basis.
 
Statistical analysis
 
Statistical analysis is performed for randomized block design; mean, range, CV% is recorded. Principal components analysis was performed to examine the contribution percentage of each parameters to the total genetic variation. Principal component analysis was carried out according to procedure described by Rao (1984).

Exploration and collection
 
Expeditions were conducted in nine mandals of Visakhapatnam and Vizianagaram districts from Eastern Ghats of Andhra Pradesh from Paderu, Araku, Hukkumpeta, Vizianagaram and Chodavaram regions collecting the 25 seed samples of horsegram germplasm. The tribal tracts of all these mandals are very rich source of germplasm of varied crops. The collection site was having 17^o and 18^o North latitude and 82oand 83o East  longitude with an altitude  ranging  from 58 m to 994 m from the mean sea level. The passport data of the germplasm accessions collected during the expeditions is presented in Table 1. The passport data showed that most of the biological status accessions are ancestral. This shows the conservation of horsegram germplasm from ancestors.
 
 
 
Morphological characterisation
 
The mean, range and morphological characterized data is presented in Table 2 and 3. Days to 50% flowering ranged from 56 to 67 days with a mean of 62 days. Days to maturity recorded a wide variation of 87 to 106 days duration with a mean of 97 days. This study revealed wide variation in early and late maturing germplasm lines. There is no much variation recorded in no. of branches per plant. Wide range of variation was observed for number of pods per plant i.e., from 29-67 pods per plant with a mean of 43.96 pods per plant. All the germplasm lines had sparsely hairy or hairy leaf and stem habit. All the germplasm lines showed green leaf colour except HG-7 which showed variegated nature. The horsegram germplasm lines showed variation for twining habit with prominent, moderate and very less twining. Seed coat colour recorded was either brown, straw brown or black. Test weight (100 seed weight) showed range of 2.0 g to 4.6 g. Dry haulm weight per plant recorded a range of 1.9 to 6.0 g. Number of seeds per pod showed a range of 5.0 to 7.0 with a mean of 5.78. Seed yield per plant (g) ranged from 2.4 to 6.8 g with a mean of 4.19 g per plant. Wide variation was observed in seed yield per plant (g); 100 seed weight (g), number of pods per plant, dry haulm weight per plant (g); number of seeds per pod and days to maturity. The results are in accordance with Chahota et al., 2005 and 2013.
 

 

 
Principal component analysis
 
Principal component (eigen value greater than one) percent variability, cumulative % variability and component loading of different characters are presented in Table 4 and 5. In the present investigation, principal component analysis identified 9 principal components contributing 100% cumulative variance. The first four factors eigen values greater than one contributed high to the total variability. The first principal component showed maximum contribution to cumulative variance (37.52%). All the parameters showed positive loading except 100 seed weight (g) which showed negative loading. The second principal component contributed 16.39% to cumulative variance. All the parameters showed positive loading except no. of branches per plant and number of pods per plant. They showed negative loading. The third principal component contributed 12.47% to cumulative variance. All the parameters showed negative loading except plant height, no. of pods per plant and no. of seeds per pod.  The fourth principal component contributed 11.21% towards cumulative variance. All the parameters showed negative loading except days to 50% flowering number of pods per plant, days to maturity and no. of seeds per pod. The results are in accordance with Bhartiya et al., 2017 and Gupta et al., 2010.
 

 

       
In the first principal component, plant height (19.29%), dry haulm weight (g) (18.95%), seed yield per plant (g) (16.24%) variables contributed highest contribution. The results are in accordance with Gupta et al., 2010.
       
The biplot (Fig 1) shows HG-24 (3.96), HG-7 (2.86); HG-19 (2.03); HG-15 (1.60) and HG-22 (1.58) recorded highest positive scores. The biplot also shows that the genotypes HG-5, HG-10, HG-3, HG-16, HG-8, HG-4, HG-10, HG-24 and HG-7 has wide divergence which may be further adopted in the breeding programme for horsegram improvement programme. Among all the active variables (yield characters) plant height, dry haulm weight per plant and seed yield per plant recorded high score.
 

The twenty five germplasm lines collected from the tribal tracts of Andhra Pradesh showed the predominance of ancestral biological status of accession. The seed yield per plant recorded a range of 2.40 g to 6.80 g and the days to maturity recorded a range of 87 to 106 days. The principal component analysis showed that all the variables except 100 seed weight (g) showed positive loading. Among all the variables plant height (cm), dry haulm weight (g) and seed yield per plant recorded maximum percentage of contribution in the first principal component.  The genotypes HG-24, HG-7, HG-19, HG-15, HG-22 recorded highest positive scores. The genotypes HG-5, HG-10, HG-3, HG-16, HG-8, HG-4, HG-10, HG-24 and HG-7 has shown wide divergence which may be further adopted in the breeding programme for horsegram improvement.

The authors are highly thankful to the ANGRAU for the funding, the project in collection of germplasm of horsegram and department of Agriculture in co-ordinating the expedition.