69 J. Hortl. Sci. Vol. 14(1) : 69-72, 2019 Short Communication Effect of trichomes in cowpea on infestation by spotted pod borer, Maruca vitrata (Fab.) (Lepidoptera: Crambidae) *Nasiya-Beegum A.N. and Madhu Subramanian Department of Agricultural Entomology Kerala Agricultural University, Thrissur *Email : nasiyakau@gmail.com ABSTRACT Trichomes are the morphological features present on the surface of plants, which provide resistance to several insect pests. A pot culture experiment with 48 cowpea accessions were conducted to evaluate the effect of trichomes in cowpea on infestation by spotted pod borer, Maruca vitrata. Significant variation in terms of damage to pods due to spotted pod borer was observed. The number of trichomes per unit area was significantly and negatively correlated (-0.441) with per cent damage. However, the length of trichomes on pods has no significant correlation with per cent damage. Key words: Trichomes, resistant, cowpea, pod, Maruca vitrata Cowpea is an important leguminous crop cultivated throughout the tropics and subtropics. The legume pod borer, Maruca (testulalis) vitrata (Geyer) is a serious pest of grain legumes. This insect is a major constraint in increasing the production and productivity of grain legumes.The pod borer larvae feed on buds, flowers and pods by webbing them. Tr ichomes a r e the one of the most impor ta nt morphological characters associated with insect resistance across the plant kingdom. It is a special c ha r a c t er, involving sever a l f a ct or s s uc h a s distribution of the hairs, the density of hair cover, t he lengt h of t he ha ir s , t yp e of ha ir s et c . Ovipositional and feeding non-preference, due to t he p r es enc e of s imp le t r ic homes , ha s b een reported to be one of the mechanisms of resistance in c owpea a ga inst M. v it ra ta . Tr ichomes on cowpea pods can affect the activity of insects by mechanical means. Pubescence or trichome density is one of the most impor ta nt physical cha r acters a ssocia ted with insect resistance across the plant kingdom. It is a complex character, involving several factors like the distribution of the hairs, the length of the hairs, the density of hair cover, disposition of hairs and the t yp e of ha ir s ( Ver ma a nd Af z a l, 1 9 4 0 ) . Ovipositional non-preference, due to the presence of trichomes, has been reported to be one of the mechanisms of resistance of cowpea to M. vitrata. Forty - eight accessions of cowpea comprising of twenty - nine accessions from National Bureau of P la nt G ene t ic R es ou r c es ( I C A R - N BP G R ) R egiona l St a t ion, J odhp u r, R a ja s t ha n, f ive a c c es s ions f r om Univer s it y of A gr ic u lt u r a l Sciences (UAS), Bengaluru, ten varieties released from KAU and one accession each from Vegetable and Fruits Promotion Council Keralam (VFPCK), Thiruvananthapuram, Indian Institute of Vegetable Resea rch (ICAR - IIVR), Va ra nasi as well a s Hor t ic ult ur e C ollege a nd R es ea r ch I nst it ut e, Per iya kula m wer e eva lua ted for r esista nce to spotted pod borer. All agronomic practices were f ollowed a s p er P a c ka ge of p r a c t ic es recommendations (KAU, 2011). These genotypes constituted the treatments in the experiment. The experiment was laid out in Completely Randomized D es ign ( C R D ) wit h 4 8 t r ea t me nt s a nd 1 0 replications, with one polybag containing one plant constituting one replication. 70 Nasiya-Beegum and Madhu Subramanian J. Hortl. Sci. Vol. 14(1) : 69-72, 2019 Table 1. Extent of damage by Maruca vitrata in cowpea accessions Accessions Per cent damaged pods Trichome length Trichome density IC 39922 1.54 0.06 74.67 IC 52107 A 2.67 0.05 185.34 KM – 5 8.06 0.06 48.00 C – 152 42.65 0.07 88.60 Kanakamony 8.24 0.07 235.34 PKM – 1 15.00 0.07 16.34 EC 100092 0.00 0.04 123.34 IC 2196 1.25 0.08 180.67 IC 39916 2.38 0.18 82.34 IC 26029 5.88 0.12 113.67 Palakkadanthandanpayar 0.00 0.23 89.34 IC 26048 0.00 0.11 96.34 Anaswara 31.90 0.05 67.34 IC 2196 9.02 0.09 213.00 IC 10810 13.64 0.06 185.00 IC 39870 3.70 0.15 17.67 TVX – 944 2.08 0.07 255.34 EC 300039 1.12 0.09 127.34 IC 52094 15.56 0.08 31.00 IC 39945 0.00 0.08 108.67 IT – 3895 – 1 16.42 0.25 72.34 Vyjayanthi 17.43 0.11 15.00 IC 20431 5.26 0.04 33.00 Sreya 6.25 0.07 186.00 IC 9883 1.34 0.07 114.34 Hridya 0.65 0.06 147.67 IC 20720 2.35 0.07 91.00 IC 2918 0.00 0.06 96.34 KBC – 2 0.00 0.07 130.34 IC 19797 10.34 0.05 51.00 Mysore Local 12.00 0.05 212.00 IC 7832 10.53 0.08 96.67 IC 39921 3.70 0.06 155.00 IC 52105 5.83 0.07 88.67 71 Trichomes and borer infestation in Maruca Kashikanchan 21.84 0.06 66.00 IC 52128 1.09 0.06 50.34 EC 98668 0.00 0.13 123.45 IC 39947 0.00 0.07 91.67 IC 20645 0.00 0.06 32.00 IC 19778 12.99 0.10 31.67 VellayaniJyothika 18.28 0.10 39.34 Malika 26.61 0.00 0.00 Sharika 35.16 0.09 21.67 Bhagyalakshmy 47.95 0.07 15.00 EC 101216 1.03 0.07 224.34 IC 52110 0.00 0.05 135.34 IC 52118 0.00 0.07 154.67 Lola 47.47 0.25 18.34 Correlation 0.183 -0.441* *Correlation is significant at 0.05 level (2-tailed) Trichome length was measured by Leica-EZ stereo microscope equipped with Leica Application Suite (LAS) image analysing software. Length of ten trichomes on pods selected at random, the average was worked out. The counts of trichomes on the pod surface was made from an area of 6.25 mm2 using a Radical Stereo Zoom microscope at 35x magnification, after marking out an area of 2.5 x 2.5 mm2 over the excised pod. Counts were taken from three different points on each pod and the average was worked out and presented in Table 1. Based on the density of trichomes, the accessions were classified into: 1. Glabrous - 0 to 50 trichomes per 6.25 mm2 unit ar ea 2. Sparsely pubescent - 51 to 100 trichomes per 6.25 mm2 unit area 3. Pubescent - 101 to 150 trichomes per 6.25 mm2 unit area 4. Densely pubescent - more than 15 trichomes per 6.25 mm2 unit area T he va riety Lola r ecor ded maximum tr ichome lengt h of 0 . 2 5 mm a nd wa s on p a r wit h Palakkadanthandanpayar with a mean trichome lengt h of 0 . 2 5 mm a nd 0 . 2 3 mm. Bot h t he a cc essions wer e significa ntly super ior to the r ema ining a c c es s ions whic h r ec or ded mea n trichome length of ranging from 0.04 to 0.01mm. The accessions varied significantly in terms of trichome density. The number of trichomes varied from 16.34 per 6.25 mm2 in PKM - 1 to 288.67 per 6.25 mm2 in TVX – 944. High trichome density was also observed in Kanakamony, Mysore local, Sreya and Anaswara, with 235.34, 212, 186 and 167.34 trichomes per 6.25 mm2 respectively. All these accessions were sta tistically on pa r with ea ch other but differ ed significa ntly fr om the remaining genotypes. PKM - 1, which recorded the lowest trichome density of 16.34 per 6.25 mm2 was followed by Bhagyalakshmy, Lola, IC 52105, EC 300039, IC 20645, IC 20431, Vellayani Jyothika and Palakkadanthandanpayar with trichome density of 17.34, 18.34, 18.67, 27.34, 32, 33, 39.34 and 49.34 trichomes per 6.25 mm2 respectively. All these nine accessions were statistically on par with each other but differed significantly from the remaining genotypes. The remaining accessions except Malika had trichome density ranging from 66. 00 to 147. 67 per 6. 25 mm2. Ba sed on the J. Hortl. Sci. Vol. 14(1) : 69-72, 2019 72 dens it y of t r ic homes , t he a c c es s ions wer e cla ssified into: Densely pubescent, pubescent, sparsely pubescent and glabrous. The length of the trichomes had positive correlation (0 . 18 3) with per c ent da ma ge. However, t he c or r ela t ion wa s not s ignif ic a nt . N u mb er of t r ic homes o n p ods ha d s ignif ic a nt nega t ive correlation (-0.441) with per cent damage due to spotted pod borer. The length of trichomes, which ranged from 0.04 mm in EC 100092 to 0.25 mm in Lola, did not show a ny significa nt va r ia tion a mong the dif fer ent a ccessions. A significa nt cor r ela t ion bet ween trichome length and per cent pod damage could not be observed in the study. Sunitha et al (2006) however, ha d ob s er ved s ignif ic a nt nega t ive correlation (-0.097) between trichome length on pods and pod borer damage in pigeon pea. Trichome density varied from 16.34 per 6.25 mm2 in PKM-1 to 288.67 per6.25 mm2 in TVX – 944. High trichome density ra nging from 167. 34 to 235.34 trichomes per 6.25 mm2 was also observed in K a na ka mony, M ys or e loc a l, S hr eya a nd Ana swa r a . T he lowes t t r ichome dens it y wa s recorded in PKM-1 (16.34/6.25 mm2), followed by Bhagyalekshmi, Lola, IC 52105, EC 300039, IC 2 0 6 4 5 , I C 2 0 4 3 1 , Vella ya niJ y ot hika a nd Palakkadanthandanpayar with 17.34, 18.34, 18.67, 27.34, 32, 33, 39.34 and 49.34 trichomes per 6.25 mm2, r es p ec t ively. A c c es s ions s u c h a s Kanakamony, Sreya, Hridya, Mysore local etc., wit h higher p u b es c enc e s u ff er ed lower p es t inc idenc e. I t wa s a ls o not ew or t hy t ha t Bhagyalakshmy and Lola, with lowest values for trichome density also observed per cent damage 41.04 and 28.99 per cent, the highest in the present study. Tr ichomes ar e important components of plant defense against insect attackand contribute to a nt ix enosis in cr op p la nts s uc h a s cott on (Dhaliwal and Arora, 2001). This was observed in the present instance a lso, with the number of trichomes on pods being negatively correlated with total damage. Oghiakhe (1995) also had reported that pubescence in wild and cultiva ted cowpea a dver sely a ffected oviposition, mobility, food consumption and utilization by the legume pod borer. Nasiya-Beegum and Madhu Subramanian J. Hortl. Sci. Vol. 14(1) : 69-72, 2019 (MS Received 10 September 2017, Revised 09 September 2018, Accepted 21 February 2019) REFERENCES Dhaliwal, G. S. and Arora, R. (2001). Integrated Pe s t M a n a g e m e n t : C o n c e p t s a n d Approaches. Kalyani Publ., New Delhi. 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