Genetic Diversity for Yield and Yield Contributing Characters of Short Statured Maize Inbred Lines

Genetic diversity is one of the useful tools to select appropriate lines for hybridization. Twenty short-statured maize inbred lines were taken for present study, which were collected from CIMMYT India and Mexico through Plant Breeding Division, Bangladesh Agricultural Research Institute (BARI), Gazipur. This experiment was conducted from November 2015 to April 2016 to identify parental lines to produce single cross short statured maize hybrids. From the genetic diversity studies, the importance of both additive and non-additive gene actions for the expression of yield and yield contributing characters were found. Values of vector I and II revealed that both the vectors had positive values for date of silking, plant height, rows/cob, grains/row and yield. These results indicated that these five characters had highest contribution towards divergence. Based on the relative magnitude of D 2 values; 20 inbred lines were grouped into five clusters. Seven inbred lines were selected on the basis of genetic diversity and per se performance which will be crossed separately in a half-diallel fashion to develop hybrids.


Introduction
"Maize (Zea mays L., 2n = 20)'' is one of the most important cereal crops in the world. It is a major food, feed and industrial crop both in developed and developing countries. The area, production and yield of maize have increased many The experimental fields were prepared by ploughing with tractor followed by harrowing and laddering to bring desirable tilth. Fertilizers recommended for inbred were applied @ 120, 80, 80, 20, 5, 1 kg•ha −1 of N, P 2 O 5 , K 2 O, S, Zn, B, respectively. One third of nitrogen and the whole amount of other fertilizers were applied to the soil at the time of final land preparation. The experiments for each group of genotype were planted in two rows of 5 m. length, row to row and plant to plant spacing of 60 cm and 20 cm, respectively, Sowing was done in furrows with two seeds per hill. The seedlings emerged five to seven days after sowing.
Seedlings were thinned keeping one seedling per hill after two weeks of emergence.
Standard agronomic practices were followed in trial management [13] and necessary intercultural operations were done during the crop growing period to ensure the normal growth and development of the plants.
Ten randomly selected competitive plants at field maturity (5 from each row in a plot of each genotype) excluding any plant surrounding by a missing hill were used for receding observations on the following parameters: days to tasseling (DT), days to silking (DS), plant height (PH), ear height (EH), ear length (EL), ear diameter (ED), number of rows cob −1 (R/C), number of seeds row −1 (S/R), thousand grain weight (TGW), grain yield plant −1 (Y/P).

Results and Discussion
Mean performance of short statured maize inbred lines Mean performance of the inbred lines presented in Table 1. The highest grain yield was observed from maize line 16, followed by maize lines 13, 20, 1 and 2.
Yield components such as ear length and diameter, number of kernels per ear and thousand grain weights were found higher in lines 1, 2, 13, 14, 19, 20 but some of them were late in anthesis time and medium in plant stature.   Construction of scatter diagram of 20 short statured maize inbred lines The analysis of variance showed significant variations among all the inbred lines for all the ten characters studied. Based on the values of principal component scores 2 and 1 obtained from the principal component analysis, a two-dimensional scatter diagram (Z 2 -Z 1 ) using component score 1 as X-axis and component score 2 as Y-axis was constructed, which has been presented in Figure 1. The genotypes were distributed in 5 clusters based on their position in scatter diagram suggesting sufficient variabilities among them. It was also revealed that the inbred lines of cluster III was more diverse from the inbred lines of cluster II. This was an illustration by [14] [15].
Cluster analysis of 20 short statured maize inbred lines Clustering pattern could be utilized in choosing parents for cross combination that could be produced variability for selection [13]. Genetic diversity of 20 inbred lines was studied using Mahalanobis's D 2 statistics. All the 20 inbred lines were grouped into 5 clusters. The distribution pattern indicated that maximum 7 inbred lines were included in cluster III followed by 6 in cluster IV. The remainders have been distributed in three clusters: 2 in each cluster I and II, 3 in cluster V. Clusters III and IV comprised 35% and 30% of the total inbred lines ( Table 2). [16] classified five in divergence of maize inbreds, [17] six clusters of sixty four maize inbreds, [18] seven clusters of thirty nine maize genotypes, [19] nine clusters of forty three maize inbred line [20]   Principal Coordinate Analysis (PCO) was done to get inter genotypic distances. The highest inter genotypic distance (1.683) was observed between the lines L20 and L5 followed by the lines L16 and L5 (1.646) and lines L5 and L13 (1.644) ( Table 4). The lowest distance was observed between the lines L3 and L15 (0.1897) followed by the lines L11 and L10 (0.2688) and lines L15 and L12 (0.2701) ( Table 5). The difference between the highest and the lowest inter genotypic distance indicated the existence of variability among 20 inbred lines of maize.
Average intra and inter cluster distance of 20 short statured maize inbred lines The inter cluster distance ( Table 6) was maximum between cluster II and V (28.19) followed by cluster II and IV (24.62) and then between cluster I and IV (19.72). While the inter cluster distance was minimum between cluster I and III (9.18) followed by cluster IV and V (9.65) and then between cluster II and III (12.09). The maximum value of inter cluster distance indicated that the lines belonging to cluster II and V were far diverged. Similarly the higher inter cluster   values between cluster II and IV, cluster I and V, I and IV indicated the lines belonging to each pair of cluster we real so far diverged. The intra-cluster distances were calculated from these inter-genotypic distances as suggested by [24]. The enormity of the intra-cluster distances didn't recorded proportional to the number of genotypes in each clusters (Table 6). In the present study it was found that although cluster III composed of largest number of lines, 7 ( Table 2) but intra-cluster distance was not necessarily the highest ( Table 6). The highest intra-cluster distance was recorded in cluster II (1.214) containing 2 lines (L5, L12) followed by cluster I (1.044) also containing 2 lines (L6 and L18). The least intra-cluster distance was observed in cluster IV (0.6577) consisting of 06 lines (L1, L2, L09, L13, L14 and L16).
Cluster means of 20 short statured maize inbred lines Cluster mean for 10 characters are presented in Table 7. Cluster I composed of two lines (L6 and L18), scored highest mean for date of tasseling (102.00), date of silking (106.50), plant height (98.50), ear height (32.30) and ear diameter (3.92). Second highest mean was obtained from character Rows/cob (12.40).
Cluster II composed of two lines (L5 and L12) gave highest mean for rows/cob (13.20) and seed/row (18.35), second highest mean was obtained from character ear length (9.55).
Cluster IV composed of six lines (L1, L2, L9, L13, L14 and L16) and gave highest mean for yield/plant (280.00) and second highest mean value were obtained from ear diameter (3.86) and thousand grain weight (286.67).
Cluster V composed of 3 lines (L17, L19 and L20) and was found to give highest mean for 1000 seed wt. (313.33) and ear length (10.50), second highest mean was found for plant height (88.90), ear height (30.77).
The highest mean values for some expected yield contributing traits were identified in cluster I, II, IV and V, the second highest values of some desirable traits were grouped in cluster III, IV. Therefore, selection for higher yield can safely done from these clusters.
Latent vectors of 20 short statured maize inbred lines Contribution of characters towards divergence of the genotypes obtained from principal component analysis (PCA) was presented in Table 8. Values of vector

Conclusions
Among the 20 short-statured inbreds, the performance of inbred lines 16 and 13 showed high yield with different yield contributing traits. Plant and ear height was found the highest in inbred line18 followed by 19 and 09 and it was found lowest in 05 followed by 07 and 17. Plant height ranged from 49.30 cm to 122.30 cm and ear height ranged from 12.7 cm to 47.0 cm. In all the lines, ear placement was at or near the midpoint of the plant which was a desirable character.
In cluster analysis maximum of 07 short-statured inbred lines were included in cluster III followed by 06 in cluster IV. These two clusters contained 65% of the total inbred lines. The inter-cluster distance was maximum between cluster II and V (28.19) followed by cluster II and IV (24.62) and then between cluster I and IV (19.72). While the inter-cluster distance was minimum between cluster I and III (9.18) followed by cluster IV and V (9.65) and then between cluster II and III (12.09). Cluster II and III gave the lowest mean for plant and ear height.
The highest cluster mean for some desired yield contributing characteristics were observed in cluster I, II, IV and V, second highest value of some desired character recorded in cluster III, IV. Both the vectors I and II had positive values for yield per plant, days to silking, plant height, rows per cob, seeds per row indicated that these five characters had the highest contribution and had negative value for the date of tasseling, ear length and ear diameter indicated that these three characters had the lowest contribution towards the divergence among 20 inbred lines.
Out of twenty inbreds, seven short statured maize inbred lines such as SP05, SP06, SP03, SP04, SP02, SP01, SP07 were selected for crossing and evaluation considering overall performance, yield performance, cluster distance, cluster mean and contribution of the characters towards divergence.

Conflicts of Interest
There were no conflicts of interests.