17 J. Hortl. Sci. Vol. 15(1) : 17-26, 2020 Original Research Paper Assessment of Genetic Divergence in Long Day Onion (Allium cepa L.) through Principal Component and Single Linkage Cluster Analysis Singh S.R., Ahamed N., Srivastava K.K., Kumar D. and Yousuf S. ICAR-Central Institute of Temperate Horticulture, Old Air Field Rangregth, Srinagar - 190 007, Jammu and Kashmir, India Email : srajparmar@gmail.com ABSTRACT To assess the nature and magnitude of genetic diversity in long day onion germplasm by using the principal component analysis and single linkage cluster analysis an experiment was carried out with 34 onion genotypes. High coefficient of variation with wide range in traits indicated an appreciable variability in germplasm. Genotypes were classified into seven principal components having Eigen value > 1, cumulatively accounted for 83.87% of total variability. Principal Component - I contributed for 24.73% of total variation for followed by principal component-II (15.27%). PC-I had high positive loading for bulb weight (0.401), marketable yield (0.338), total bulb yield (0.401) and PC-II had high positive loading for plant height (0.412), PC-III for high T.S.S. (0.276) PC -IV for A grade bulbs (0.436), PC-V for polar diameter of bulbs (0.514), PC-IV negatively loaded with purple blotch (-0.461) and PC-VII for narrow neck thickness (-0.515). Plotting PC-I aganist PC-II differenciated CITH-O-13, CITH-O-4, CITH-O-22, CITH-O-19, CITH-O-9, CITH-O-6 and CITH-O2 as most divergent genotype.On the basis of single linkage cluster means cluster-I was most importent for average bulb weight, minimum bolters, high marketble bulb percentage high marketable and total bulb yield whereas cluster -II was important for maximum nuber of leaves/plant and minimum neck thicknes. Highest inter-cluster distance was observed between cluter II and Cluster-I(873.5% ).Most divergent genotypes with high inter cluter distance could be the most appropriate parents for crop impovement in onion. Key Words: Genetic diversity, Onion, Principal component analysis, Single linkage cluster analysis INTRODUCTION Onion is an important vegetable crop used by all the sections of people,round the year throughout the world for its distinct flavour and health healing properties. It is a photosensitive crop and forms bulbs at certain day length. Long day onion requires 14 hours or more day length to initiate the bulbing. In India, majority of growing area is under short day onion except in hillyregion. Long day onion is grown in temperate region of India with productivity ranging from 10 to 23 t/ha.Though it covers large temp er a te a r ea fr om Ja mmu a nd K a shmir to Ar u na c ha l P r a des h b u t ef f or t s o n va r iet a l improvement programme on long day onion are ver y limited. There is no commercial long day variety available for cultivation except some old introductions like Yellow Globe and Brown Spanish. F a r mer s u s e t heir own s eed wit h ou t c a r ing isolation distance to maintain the purity which leads to a great variability in shape and size of bulb with inherent low yield. T he ma gnitu de of genet ic diver s ity in onion germplasm is a critical component in breeding for new cultiva r. Selection of genetica lly diver se parents in breeding programme on the basis of divergence would be more promising to get the heterotic F1, and to create a broad spectrum of variability in segregating generation (Meena and This is an open access article d istributed under the terms of Creative Commons Attribution-NonCommer cial-ShareAl ike 4.0 International License, which permits unrestricted non-commercial use, d istribution, and reproduction in any med ium, provide d the original author and source are credited. 18 J. Hortl. Sci. Vol. 15(1) : 17-26, 2020 Singh et al. Bahadur, 2015). Presence of genetic diversity play a vital role in plant breeding for getting higher yield, uniformly disired quality and resitance to b iot ic a nd a b iot ic s t r es s es . A s ys t ema t ic understanding of gentic diversity in different traits is essentia l for ta rgeted br eeding pr ogr amme. T her e a r e nu mer ic a l t a x onomic t ec hniqu es available to classify the variation pattern at inter and intra specific level (Ario and Odulaza, 1999). Mult iva r ia te a na lys is is a n effect ive tool for characterization and classification of plant genetic resources, when a large number of accessions are assessed for several traits (Peter and Matrinelli, 1989). Different type of multivariate analysis such as principal component analysis (PCA) and single linka ge c lu st er a na lysis (S LCA) a r e u sed to identify groups of accessions that have desirable traits for breeding and assessing the pattern of variation in germplasm collection. PCA enables easier understanding of impact and relationship among the different traits. However PCA alone wou ld not give a n a dequ a t e c ha r a c t er representation in term of relative importance when multiple characters are considered simultaneously (Shalini et al., 2003). To complement the results of such multiva r ia te a na lysis, Single Linka ge Cluster Analysis(SLCA) is employed to classify the varia tion. It is a n a gglomer ative technique which shows t he p a tt er ns of ex a c t genot yp e position in population. (Ariyo and Odulaza, 1999) by sorting them in distinct group.Thus this study is aimed to identify the major characters responsible for variation among the onion genotypes with a view to group accessions and for identifying the potential parental stocks within the group of local germplasm by employing the multivariate analysis. MATERIALS AND METHODS Thirty four long day onion accessions (Allium cepa L.) including two varieties collected from growing hot spot of Kashmir valley and conserved at active ger mpla sm sit e of IC AR- Cent r a l Ins tit ute of Tempera te Horticultur e, Sr ina ga r (J&K) wer e evaluated (Table 1). The seedlings of 45 day old were transplanted in main field during rabi season. Ea ch accession was grown in ten rows of two metre length with a spacing of 10x15 cm. The experiment was conducted in randomized block design wit h thr ee r ep lica tions . Geogr a phic a l position of the experimenta l site lies between latitude of 34005 N and longitude of 74050 E at an altitude of 1640 MSL. The average maximum and minimum temp er a t u r e wer e 1 9. 63 0C , 6. 52 0 C respectively with annual precipitation of 160.72 mm and relative humidity 58.35%, evaporation 2.45mm. The soil characteristics viz. pH= 6.81 and EC = 0. 36 dSm-1 wer e r ecorded dur ing the cr opping sea son. Recommended unifor m agronomic and cultural practices were adopted to obtain better expr ession of phenotypic char acters. Data was recorded on nineteen quantitative traits. Disease severity rating was measured on 0-5 scale - (0 grade - No disease, 1 grade - 1-10%, 2 grade -11- 20%, 3 grade -21-30%, 4 grade -31-50% and 5 grade -51-100%). Whereas, pest (thrips) damage (1-5 scale) - (1 -1-20% foliage damage, 2- 21-40 foliage damage, 3-41-60% foliage damage, 4-61- 80% foliage damage and 5-81-100% foliage. The genotypes with <5% infestation was considered immu ne, 6 - 1 0 % inf es t a t ion r esis t a nt , 1 0 - 2 0 infestation moderately resistant, 21-40% infestation moder a t ely s u c ep t b le, 4 1 - 6 0 % i nf es t a t ion susceptible >60% infestation considered highly susceptible. Da ta collected on the quantitative characters were analyzed using SAS Microsoft Windows 9.2 (SAS Institute, 2011), employing the method outlined by Steel and Torrie (1980) using statistical XL STAT-2011. Principal Component Ana lysis a nd Single Linkage Cluster Ana lysis (SLCA) were used for the determination of genetic var iation and percenta ge simila rity within the genot yp es . E igen - Vec t or s a nd p r inc ip a l component score were used to assess the relative dis c r imina t or y p ower of it s a x i s a nd t heir associated characters. The cluster procedure was used to produce distinct groups of 34 genotypes on the basis of genetic relationship while using the character variation. Average intra-cluster distance wa s c a lc u la ted by t he f ollowing f or mu la a s suggested by Singh and Choudhary (1985). SLCA summa r ized the position of a ccessions into a dendogramat an interval of 5% level of dissimilarity s t a r t ing f r om 1 0 0 % level of di s s imila r it y (Kendall, 1980). 19 Assessment of genetic divergence in long day onion (Allium cepa L.) T ab le 1. A cc es si on s w it h th ei r ge og ra ph ic al i nf or m at io n us ed i n st ud y G en ot yp e C ol le ct io n L at itu de L on gi tu de A lti tu de G en ot yp e C ol le ct io n L at itu de L on gi tu de A lti tu de si te (M et er ) si te (M et er ) C IT H -O -1 B ud ga m 34 .6 30 74 .0 40 31 99 .9 9 C IT H -O -1 7 Sr in ag ar 34 .0 80 74 .7 90 15 85 .0 1 C IT H -O -2 B ud ga m 34 .6 30 74 .0 40 31 99 .9 9 C IT H -O -1 8 B ar am ul la 34 .1 98 0 74 .3 60 15 90 .0 0 C IT H -O -3 B ud ga m 34 .6 30 74 .0 40 31 99 .9 9 C IT H -O -1 9 B ar am ul la 34 .1 98 0 74 .3 60 15 90 .0 0 C IT H -O -4 B ud ga m 34 .6 30 74 .0 40 31 99 .9 9 C IT H -O -2 0 B ar am ul la 34 .1 98 0 74 .3 60 15 90 .0 0 C IT H -O -5 B ud ga m 34 .6 30 74 .0 40 31 99 .9 9 C IT H -O -2 1 B ar am ul la 34 .1 98 0 74 .3 60 15 90 .0 0 C IT H -O -6 B ud ga m 34 .6 30 74 .0 40 31 99 .9 9 C IT H -O -2 2 B ar am ul la 34 .1 98 0 74 .3 60 15 90 .0 0 C IT H -O -7 B ud ga m 34 .6 30 74 .0 40 31 99 .9 9 C IT H -O -2 3 B ar am ul la 34 .1 98 0 74 .3 60 15 90 .0 0 C IT H -O -8 G an dh ar ba l 34 .2 30 74 .7 80 16 19 .1 0 C IT H -O -2 4 Sh op ia n 34 .8 10 75 .0 10 20 57 .0 0 C IT H -O -9 G an dh ar ba l 34 .2 30 74 .7 80 16 19 .1 0 C IT H -O -2 5 Sh op ia n 34 .8 10 75 .0 10 20 57 .0 0 C IT H -O -1 0 G an dh ar ba l 34 .2 30 74 .7 80 16 19 .1 0 C IT H -O -2 6 B ad ip or a 34 .5 00 74 .6 80 15 78 .0 0 C IT H -O -1 1 G an dh ar ba l 34 .2 30 74 .7 80 16 19 .1 0 C IT H -O -2 7 B an di po ra 34 .5 00 74 .6 80 15 78 .0 0 C IT H -O -1 2 G an dh ar ba l 34 .2 30 74 .7 80 16 19 .1 0 C IT H -O -2 8 K ul ga m 33 .6 50 75 .0 20 17 38 .8 8 C IT H -O -1 3 Sr in ag ar 34 .0 80 74 .7 90 15 85 .0 1 C IT H -O -2 9 K ul ga m 33 .6 50 75 .0 20 17 38 .8 8 C IT H -O -1 4 Sr in ag ar 34 .0 80 74 .7 90 15 85 .0 1 C IT H -O -3 0 K up w ar a 33 .6 50 75 .0 20 17 38 .8 8 C IT H -O -1 5 Sr in ag ar 34 .0 80 74 .7 90 15 85 .0 1 C IT H -O -3 1 K up w ar a 33 .6 50 75 .0 20 17 38 .8 8 C IT H -O -1 6 Sr in ag ar 34 .0 80 74 .7 90 15 85 .0 1 C IT H -O -3 2 Sr in ag ar 34 .0 80 74 .7 90 15 85 .0 1 C or al R ed IC A R -D O G R P un e - - B ro w n I C A R -D O G R P un e (c he ck ) Sp an is h J. Hortl. Sci. Vol. 15(1) : 17-26, 2020 20 RESULTS AND DISCUSSION The genotypes evaluated for all horticultural traits va ried significantly (Table 2). The phenotypic variability expressed by range, standard deviation, and coefficient of variation. The plant height ranges fr om 63. 33 to 91. 66 cm. Genotype CITH-O-9 recorded highestplant height, whereas CITH-O-32 recorded lowest plant height (63.33 cm). Number of leaves ranged from 6.33 ( CITH-O-9 ) to 14.0 cm (CITH-O-19. Polar diameter of bulb ranged from 5.18cm (CITH-O-7) to 11.97cm (CITH-O- 13). Equatorial diameterof bulb ranged from 5.87cm (CITH-O-5) to 11.08 cm (CITH-O-8). Polar and equatorial diameter ratio reflects the bulb shape Singh et al. J. Hortl. Sci. Vol. 15(1) : 17-26, 2020 Table 2. Variation in quantitative traits of onion accessions Plant height (cm) 63.33 CITH-O-32 91.66 CITH-O-9 80.09 5.92 12.92 No. of Leaves/ plant 6.33 CITH-O-9 14.00 CITH-O-19 9.87 1.66 23.71 Polar diameter (cm) 5.18 CITH-O-7 11.97 CITH-O-13 7.44 1.23 20.58 Equatorial diameter (cm) 5.87 CITH-O-5 11.08 CITH-O-8 8.52 1.15 20.85 Polar Equatorial diameterratio 0.55 CITH—O-11 2.03 CITH—O-4 0.89 0.26 25.82 Neck thickness (cm) 0.42 CITH-O-7 2.46 CITH-O-19 0.96 0.38 30.56 A Grade bulb (%) 12.00 CITH-O 86.11 CITH-O-12 58.71 15.95 37.05 B Grade bulbs (5) 0.00 CITH-O 34.55 CITH-O 13.96 10.39 60.16 C Grade bulbs (%) 0.00 CITH-O 33.00 CITH-O 6.53 8.42 51.04 Doubles (%) 0.00 CITH-O 34.28 CITH-O 16.05 11.48 66.97 TSS % 0.36 CITH-O-5 16.00 CITH-O-29 10.92 4.36 54.51 Average Bulb weight (gm) 154.51 CITH-O-29 470.30 CITH-O-9 289.08 82.29 34.99 Purple Blotch (%) 7.00 Brown Spanish 30.71 CITH-O-29 19.52 50.88 33.13 Thrips/plant 7.66 CITH-O-17 31.00 CITH-O-6 24.26 5.44 35.12 Downy mildew (%) 13.48 CITH-O-9 30.50 CITH-O-2 20.80 4.92 32.25 Bolters (%) 0.00 CITH-O-9 3.66 CITH-O-11 0.91 1.10 60.31 Marketable bulbs (%) 48.26 CITH-O-9 100.00 CITH-O-28 82.35 12.60 25.20 Marketable yield (q/Ha) 331.28 CITH-O-9 1212.56 CITH-O-31 765.09 251.74 41.52 Total Yield (q/h) 494.45 CITH-O-9 1505.06 CITH-O-31 925.07 263.32 34.99 Characters Range Mean Standard deviation CV (%) Minimum Maximum Value Genotype Value Genotype 21 which is an important parameter indirectly related to yield storage life and market preference. The bulbs of genotype having < 1 Polar and equatorial dia met er r a t io ( P: E ) cons ider ed a s fla t a nd genotypes having P: E ratio 1 considered globe and those having P: E r atio> 1 were considered as torpedo. Genotype CITH-O-11, had P: E ratio 1, whereas CITH-O-4, CITH-O-32 and CITH-O-13 have < 1 P: Eratio and remaining genotypes were having >1 P: E r atio. Neck thickness of bulb affects the storage life. Neck thickness ranged from0.42 to 2.46 cm. The minimum neck thickness (0.42 cm) was observed with genotype CITH-O- 7 , wher ea s C I T H - O - 1 9 ha d ma x imu m nec k thickness (2.46 cm). Bulb grade determines the market price and quality. A grade bulb ranged from 12 to 86.11 per cent (Table 3). Genotype CITH- O-12 recorded highest A grade percentage of bulbs. B grade bulb ranged from 00 to 34.55 per cent. Double bulbs which are major drawback in onion production ranged from 00 to 34.28 per cent. Total soluble solids important quality trait in onion ranged from 0.36 to 16 per cent. Genotype CITH-O-29 scored highest TSS (16 %) whereas minimum TSS (0.36%) was recorded with genotype CITH-O-5. Average bulb weight which is directly correlated wit h yield, r a nged f r om 1 5 4. 5 1 t o 4 7 0. 3 0g. Genotype CISH-O-9 recorded the highest average bulb weight (470.30 g) whereas smallest bulb size was recorded with CITH-O-29 (154.51 g). Foliar disease of onion is major problem in long day conditions.The incidence of purple blotch ranged from 7.00 to 30.71%. Genotype CITH-0-29 has recorded highest infestation (30.31%) whereas, Assessment of genetic divergence in long day onion (Allium cepa L.) J. Hortl. Sci. Vol. 15(1) : 17-26, 2020 Table 3. The Principal component latent vector for Eigen values and proportion of variance accounted for different components with respect of different traits Characters PC-I PC-II PC-III PC-IV PC-V PC-VI PC-VII Plant height (cm) -0.039 0.412 0.045 0.208 0.328 -0.215 0.018 No. of Leaves/ plant -0.317 0.147 0.273 -0.001 0.192 -0.043 0.014 Polar diameter (cm) -0.037 -0.315 -0.109 -0.262 0.514 -0.072 -0.162 Equatorial diameter(cm) 0.354 0.227 0.062 -0.018 -0.075 0.040 0.160 Polar Equatorial diameterratio -0.204 -0.355 -0.168 -0.138 0.398 -0.108 -0.230 Neck thickness (cm) 0.040 0.288 0.283 -0.228 0.096 0.128 -0.515 A Grade bulb (%) 0.179 -0.111 0.278 0.436 0.234 -0.187 0.083 B Grade bulbs (5) -0.208 0.034 0.346 -0.355 -0.111 0.250 0.081 C Grade bulbs (%) -0.027 -0.336 -0.302 0.041 -0.403 -0.090 0.146 Doubles (%) -0.243 0.198 -0.267 -0.325 -0.101 0.154 0.177 TSS % -0.236 -0.142 0.276 -0.214 -0.135 -0.179 0.146 Average Bulb weight (gm) 0.401 0.034 -0.029 -0.309 0.104 0.014 0.022 Purple Blotch (%) 0.055 -0.082 0.198 -0.183 0.021 -0.461 0.376 Thrips/plant -0.195 -0.170 0.305 -0.108 0.012 0.057 0.277 Downy mildew (%) -0.006 -0.137 0.158 0.221 0.156 0.660 -0.002 Bolters (%) -0.039 0.023 -0.331 0.029 0.322 0.280 0.564 Marketable bulbs (%) 0.148 -0.410 0.282 0.146 -0.098 0.137 0.030 Marketable yield (q/Ha) 0.388 -0.192 0.125 -0.199 0.025 0.083 0.063 Total Yield (q/h) 0.401 0.034 -0.029 -0.309 0.104 0.014 0.022 Eigen value 4.698 2.902 2.410 2.072 1.583 1.221 1.051 Variability (%) 24.726 15.271 12.686 10.904 8.333 6.424 5.530 Cumulative % 24.726 39.998 52.684 63.588 71.921 78.345 83.876 22 least infestation was observed with variety Brown Spanish (7%). Downy mildew infestation ranged fr om 13 . 48 to 30. 50%. T he lowest ( 13. 48%) infesta tion of downy mildew wa s obser ved in genotype CITH-0-9 whereas highest infestation of was recorded with CITH-0-2 (30.50%). Thrips is major damaging insect in long day onion. Number of thrips/plant ranged from 7.66 to 31.00 / plant. T he minimum infesta tion of thrips /pla nt wa s recor ded with genotype CITH-0-6 (7.66/plant) whereas, maximum number of thrips / plant was observed with CITH -0-17 (31.00/plant). Premature bolting a burning problem in onion ranged from 0 to 3.66 % among the genotypes evaluated. The highes t p er c ent of b olt ing wa s ob s er ved in genotype CITH-0-11 (3.66%), whereas fourteen genotypes recorded 0% bolting. Marketable bulb percenta geis a n importa nt tr ait fr om economic point of view. The percentage of marketable bulb r a nged f r o m 4 8 . 2 6 t o 1 0 0 % . T he lowes t ma r ket a b le b u lb p er c ent a ge ( 4 8 . 2 6 % ) wa s recorded with genotype CITH-09 whereas CITH- 0 - 2 8 ha d r ec or ded 1 0 0 % ma r ket a b le b u lb s . Ma r keta ble bulb yield r a nged fr om 33 1. 28 to 1212.56 q/ha. The lowest marketable bulb yield was recorded with genotype CITH-0-31 (331.28 q/ ha ) wher e a s highes t ma r ket a b l e b u lb wa s recorded with CITH-0-8 (1212.56 q/ha). Total yield ranged from 494.5 to 1505.06 q/ha. Among the genotype evaluated, CITH-09 recorded highest tota l yield, where as minimum tota l yield was observed with CITH-0-31. The genotype having the highest desirable traits may be utilised for crop improvement programme for a particular tra it. Coefficient of variation (%) reflected the extent of variationfor evaluated phenotypic traits was highest for double bulb percentage and B grads of bulbs, T. S. S a nd ma r ket a ble bu lb yield (q/h) . High coef fic ient of va r ia tion a mong st udied tr a its indica ted a n a ppr ecia ble va r ia b ility which is pr er equisite of a cr op impr ovement pr ogr a m. Similar type of variability was also reported by Arya et al. (2017). The observed variability found among the onion genotypes might be related to genetic makeup of genotype as per Kandil et al. (2010). Based on degree of divergence 34 genotypes were grouped into 7 principal component having Eigen value >1 and cumulatively accounted for 83.87% of tota l va r iability (Ta ble 4a and 4b). The PC-I contr ibuted for 24. 73% of tota l va riation wa s positively loaded with bulb weight, marketable bulb percentage, total and marketable bulb yield. It was negatively correlated with number of thrips per plant, downy mildew infestation, (%) bolters and doubles, B and C grades bulbs. The PC-II reflected 15.27% of total variability and was positively loaded with plant height, neck thickness and negatively with downy mildew infestation. The PC-III was positively loaded with T. S. S. (%), number of lea ves/pla nt a nd contributed 12.69 % of total variation. The 4 t h principal component contributed 10.90% of total variability was, associated with A grade bulb (%) and negatively correlated with purple blotch disease.The PC-V accounted 8. 33% of tota l va riation wa s positively loaded with polar diameter, Polar: Equatorial. Diameter ratios, bolter percentage and negatively loaded with C grade bulb percentage. Principal Component-VI contributed 6.42% of total variation and was positively correlated with downy mildew (%) but it was negative associated with purple blotch. PC-VII accounted for 5.53% of total variation was positively loaded with bolter percentage, purple blotch percentage, and number of thrips/plant and was negativity correlated with neck thickness. The positive and negative loading of quantitative traits reflects the positive and negative correlation trend between the components and variables suggesting that these principle components may be used to summarise the variables. The traits with largest absolute value closer to unit within first component influence the cluster more than those to lower absolute value closer to zero. Thus in present study the differentiation of genotypes in different principal component was because of high contribution of few characters rather than small contribution of each character. The desirable characters loaded positively and undesirable characters loaded negatively in first seven PC’s could be in consideration while selecting the genotype for appropriate traits and yield potential. The principal component analysis has also been used for showing the genetic diversity in many species (Ravindra et al., 2018; Singh et al., 2017). The Bi-plot of PC-I & PC-II indicated that the some isolated genotype clearly define the diversity among the evaluated germplasm. The genotype CITH-0-13, CITH-0-4, CITH-0-22, CITH-0-19, CITH-0-9, CITH- 06, CITH-O-2 and variety Coral Red were most Singh et al. J. Hortl. Sci. Vol. 15(1) : 17-26, 2020 23 Assessment of genetic divergence in long day onion (Allium cepa L.) J. Hortl. Sci. Vol. 15(1) : 17-26, 2020 divergent (Fig 1) usually is customary to select one of the important variable from these identified groups for targeted improvement programme. Hence PC-I for higher total yield, PC-II for plant height, PC-III for high T.S.S, PC-IV for maximum A Grade bulb, PC-V for wider polar diameter of bulb, PC-VI for resistance to purple blotch, PC-VII for thin Neck thickness of bulb were ideal for selection . The results of present study are useful as it furnish the information about the group where certain traits are more important, allowing breeder to execute breeding for specific target. Biological implication of principal component analysis can be quantified by contribution of different variable in each PC as revealed by Eigen vector and cluster scor e at the component axis suggest that some relationship exist among the individuals with the cluster but not provided the exact position of genotypes in groups. Based on single linkage cluster analysis genotypes were grouped into five clusters by quantifying their share and cluster means for all the traits (Table 4 a,b). T he cluster -I a nd Cluster -III a ccommoda ted maximum number of genotype (9) followed by cluster II (8), Cluster-IV (7) and cluster -V(1) contributing 26.47, 23.53, 20.58 and 2.94%, of total population respectively. On the basis of cluster means, the cluster-I was important for high TSS (15.06%), marketable bulbs percentage (92.66%) powdery mildew (8.24%) and purple loch (16.08%) resistance. Cluster-II was important for plant height (83 cm) number of leaves/plant(12), polar diameter (8.54 cm) and P:E ratio (1.54) cluster -III was important A grade bulb percentage (69.21%)whereas cluster-IV was important equatorial diameter ( 9.48 cm),minimum neck thickness (0.42 cm) thrips resistance (9.33 thrips/ plant). Cluster -V was important for average bulb weight (377.76 g) marketable yield (1109.59 q/ha) and total yield (1208.83 q/ha). The genotype of cluster having high means value of particular traits would contribute more positively in their off springs if used as a parent. Arya et al. (2017) and Singh et al. Characters Cluster-I Cluster-II Cluster-III Cluster-IV Cluster-V Plant height (cm) 63.33 83.00 79.66 79.33 80.00 No. of Leaves/ plant 7.33 12.00 10.33 8.33 11.00 Polar diameter (cm) 7.50 8.54 6.55 5.18 7.95 Equatorial diameter(cm) 7.16 5.87 9.32 9.48 8.99 Polar Equatorial diameter ratio 1.05 1.45 0.70 0.55 0.89 Neck thickness (cm) 0.98 0.66 1.21 0.42 0.88 A Grade bulb (%) 22.00 42.00 69.21 65.69 63.58 B Grade bulbs (5) 25.00 6.35 12.28 0.00 20.51 C Grade bulbs (%) 25.00 12.40 0.00 15.84 7.69 Doubles (%) 28.00 28.05 17.30 16.33 8.20 TSS % 15.06 9.50 14.00 2.23 14.10 Average Bulb weight (gm) 374.06 196.98 310.39 236.69 377.76 Purple Blotch (%) 8.24 10.26 13.09 8.39 9.10 Thrips/plant 24.66 21.33 24.00 9.33 29.00 Downy mildew (%) 16.08 19.96 20.16 18.06 17.01 Bolters (%) 0.00 1.18 1.21 2.13 0.00 Marketable bulbs (%) 92.66 71.94 82.70 83.66 91.79 Marketable yield (q/Ha) 1109.15 453.47 821.41 633.64 1109.59 Total Yield (q/h) 1197.01 630.34 993.24 757.40 1208.83 Table 4a. Cluster means for 19 characters in 34 onion genotypes based on agglomerative hierarchical clustering analysis 24 Singh et al. J. Hortl. Sci. Vol. 15(1) : 17-26, 2020 Table 4b. Grouping of 34 onion genotypes into five clusters based on agglomerative hierarchical clustering analysis Characters Cluster-I Cluster-II Cluster-III Cluster-IV Cluster-V Number of genotypes 9 8 9 7 1 % of total genotypes 26.47 23.52 26.47 20.28 2.94 Position of genotype CITH-O-1 CITH-O-4 CITH-O-5 CITH-O-7 CITH-O-29 CITH-O-2 CITH-O-14 CITH-O-6 CITH-O-13 CITH-O-3 CITH-O-16 CITH-O-10 CITH-O-15 CITH-O-8 CITH-O-21 CITH-O-11 CITH-O-17 CITH-O-9 CITH-O-22 CITH-O-12 CITH-O-19 CITH-O-18 CITH-O-24 CITH-O-20 CITH-O-25 CITH-O-27 CITH-O-30 CITH-O-23 CITH-O-28 CITH-O-32 CITH-O-31 CITH-O-26 Brown Spanish Coral Red Fig. 1.: Bi-plot for 1st and 2nd PC for genotypes of onion in relation horticultural traits 25 Assessment of genetic divergence in long day onion (Allium cepa L.) J. Hortl. Sci. Vol. 15(1) : 17-26, 2020 Table 5. Average Inter and intra cluster distance Cluster-I Cluster-II Cluster-III Cluster-IV Cluster-V Cluster-I 0.00 803.47 697.08 509.31 582.56 Cluster -II 0.00 488.05 334.36 435.95 Cluster-III 0.00 305.03 579.48 Cluster-IV 0.00 353.09 Cluster-V         0.00 Fig. 2. Dendrogram depicting genetic relationship among 34 genotypes based on horticultural traits produced by complete linkage analysis (Scale- Euclidean distance at .05) (2017) also suggest that clusters having high mean value of the traits may be used for hybridization program to get better segregates. Proximity matrix obtained, suggest the resolution for 34 onion genotype distributed in five clusters with wide range of diversity for the traits (Table 5.) The highest inter cluster distance between cluster II and Cluster I (803.47%) followed by cluster-III and I (697.8) cluster V and cluster I (582.56). Based on convention that distantly related parents give better recombinants and hybrid. It could be expected that hybridization between genotype of these cluster will results high heterotic F1, s and better recombinants in segregating generations. These genotypes of distant clustercould serve useful source of genes for different desirable traits in onion. The findings are in conformity with finding of Singh et al. (2017), Chattopadhay et al. (2015) and Ravindra et al. (2018) who reported that genotypes among the cluster having high distance 26 Singh et al. J. Hortl. Sci. Vol. 15(1) : 17-26, 2020 when used in hybridization programme will obtain a wide spectrum of variation in sergeants. Dendogram obtained from single linkage cluster analysis by using the Euclidian distance depicted the clear relationship and exact position of genotype in the clusters. All the genotype were distinct at 100 percent of dissimilarity and formed nine duster at 87% of dissimilarity, and formed five clusters at 57 of dissimilarity (Fig II). The dissimilarity ranged from 57 to 100% among the delineated genotypes enough to suggest the variability for crop improvement in onion. (Denton and Nwangburuka, 2011). Genotypes CITH-0-29, CITH-0-26, CITH—8, CITH- 0-24 and CITH-05 were divergent in cluster position on the basis of Euclidian distance which reflected higher distance among these genotypes and may be used for hybridization to get the better segregates. Singh et al., 2013 and Santara et al., 2017 also reported such variability by using the single linkage cluster analysis in Onion.This genetic diversity analysis would be useful to avoid the selecting parents from genetically homogenous cluster and maintain the broad genetic base for breeding programme in long day onion. REFERENCES Ario, O. J. and Odulaza, A. 1991. Numerical analysis of variation among accessions of okra . (A. esculentus L. Moench) Malvaceae. Ann. Bot. 67:527-531 Arya, J. S., Singh, N. Arya, P. and Kant A.2017. 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