FIELD RESISTANCE OF SESAME AGAINST PHYLLODY DISEASE TRANSMITTED BY Orosius albicinctus Distant

Selvanarayanan, V. and T. Selvamuthukumaran Department of Entomology, Faculty of Agriculture Annamalai University Annamalai Nagar 608 002, Tamil Nadu, India

ABSTRACT

Among the four promising sesame cultivars tested for their field resistance against phyllody disease, cv. TMV 4 was found less susceptible to the disease. Damage to the branches and capsules was statistically on par in all the cultivars. The insect vector, Orosius albicinctus Distant, population was minimal and could not be significantly correlated to the disease incidence in the cultivars.

INTRODUCTION

Sesame is an important oilseed crop in Southern India. Among the major constraints in the production of sesame, phyllody is a very serious disease caused by mycoplasma-like organisms (MLO) capable of inflicting up to 33.9 per cent loss in yield (Abraham et al., 1977a). The causal organism (MLO) is transmitted by the leafhopper, Orosius albicinctus Distant (Cicadellidae: Hemiptera) (Vasudeva and Sahambi, 1955; Ghauri, 1966). The affected plants are stunted, with the floral parts being modified into leafy structures. The capsules abort and open exposing the developing seeds. The crown region is bushy, with shortened internodes, tiny reduced , phylloid and buds and aborted capsules.

Though this disease has been mostly managed by controlling the vector using chemical insecticides (Rosy Emerald et al., 1996), the complete elimination of the disease is not possible. Keeping in mind the supremacy of using varietal resistance factors over conventional chemical management, the present study was focused on ascertaining the resistance potential of four promising sesame cultivars.

MATERIALS AND METHODS

The field experiment was conducted in a randomized design with five replications at a farmer’s field near Annamalai Nagar, Tamil Nadu, India. The plot size was 5 x 3 m2 with plant spacing of 30 x 15 cm. The vector population was monitored weekly by trapping in sticky traps (2/plot), 30 days after sowing onwards. The incidence of the disease on five plants per replication at random was noted weekly after 51 DAS. In addition to ascertain the severity of the disease, the percentage of branches and capsules damaged was also recorded.

RESULTS AND DISCUSSION

All the cultivars differed significantly with regard to the incidence of the disease. The lowest incidence of phyllody was observed in cv. TMV 4 while the highest incidence was detected in cv. TMV 3 followed by cv. SVPR 1 during the various periods of observation (Table 1). Abraham et al. (1977b) recorded 21.8 per cent incidence of the disease on TMV 3. Though the TMV 4 recorded minimal damage to the branches, it was statistically on par with other cultivars except on 72 DAS. All the cultivars were statistically on par with each other with respect to the capsule damage.

Leafhopper population was minimal during the early phases of the crop, to a peak on 51 DAS and declined afterwards. Leafhopper population on various cultivars was not statistically significant and could not be correlated to the incidence of phyllody on the cultivars (Table 2). Murugaesan et al. (1973) and Abraham et al. (1977a) reported that the leafhopper population within the field had no significant influence on phyllody disease incidence. The reason may be attributed to the fact that even a single leafhopper coming from the source of inoculum outside the field would have inoculated a number of plants.

Hence, it was concluded that to manage the sesame phyllody, the use of resistant / tolerant varieties like TMV 4 can be recommended instead of chemical measures, which may prove futile. Further studies on phyllody management have to be focused on exploring the vast gene pool of Sesamum spp.

REFERENCES

Abraham, E.V., K. Natarajan and M. Murugaesan. 1977a. Damage by pests and phyllody to Sesamum indicum in relation to time sowing. Madras Agric. J., 64: 298-301.

Abraham, E.V., K. Natarajan and S. Jararaj. 1977b. Investigations on the insecticidal control of the phyllody disease of sesamum. Madras Agric. J., 64: 379-383.

Ghauri, M.S. 1966. Revision of the genus Orosius Distant. (Homoptera : Cicadellidae). Bull. Br. Mus. Nat. Hist., 8: 231-252.

Murugaesan, S., C. Ramakrishnan, T.K. Kandaswamy and M. Murugaesan. 1973. Forecasting phyllody disease of sesamum. Madras Agric. J., 60: 492-495.

Rosy Emerald, J.S., A. Subramaniam and A. Janagarajan. 1996. Economics of insecticides used against sesame insect pests. Indian J. Ent., 58: 274-275.

Vasudeva, R.S. and H.S. Sahambi. 1955. Phyllody in sesamum (Sesamum orientale L.). Indian Phytopathol., 8: 124-129.

Table 1. Incidence of phyllody on certain cultivars of sesame

Percentage of incidence Percentage of branches damaged Percentage of capsules damaged Cultivars 51 DAS 58 DAS 65 DAS 72 DAS 51 DAS 58 DAS 65 DAS 72 DAS 51 DAS 58 DAS 65 DAS 72 DAS

10.00 ab 32.00 c 44.00 b 56.00 bc 26.67 46.67 66.67 83.33 b 7.53 17.95 30.99 44.04 CO 1 (14.02) (34.29) (41.54) (48.46) (25.05) (43.05) (57.90) (73.95) (10.28) (19.70) (30.51) (38.32) 14.00 ab 18.00 b 26.00 a 46.00 ab 34.00 34.00 41.33 51.33 ab 18.41 29.86 37.57 46.13 SVPR 1 (21.69) (24.64) (30.43) (42.69) (35.18) (35.18) (39.95) (45.79) (22.37) (30.02) (34.60) (39.58) 20.00 b 28.00 c 48.00 b 62.00 c 24.00 43.00 77.00 86.00 b 20.67 32.36 45.20 53.35 TMV 3 (25.97) (31.76) (43.85) (52.02) (23.31) (40.85) (67.15) (72.69) (18.41) (31.28) (42.21) (47.39) 4.00 a 10.00 a 22.00 a 38.00 a 7.33 21.33 33.33 36.33 a 12.12 13.05 27.38 33.88 TMV 4 (7.37) (16.37) (27.89) (37.98) (10.13) (21.67) (34.72) (36.95) (15.90) (16.50) (31.44) (35.52) CD (p=0.05) 14.65 5.93 6.28 6.21 NS NS NS 34.67 NS NS NS NS NS – Non significant Values mean of five replications Values in parentheses are arc sine transformed Values with different alphabets differ significantly

Table 2. Population of O. albicinctus on certain sesame cultivars Number of / trap Cultivars 30 DAS 37 DAS 44 DAS 51 DAS 58 DAS 65 DAS 72 DAS

CO 1 0.4 0.2 0.6 0.8 0.2 0.4 0.2

SVPR 1 0.6 0.4 0.4 1.0 0.4 0.2 0.2

TMV 3 0.2 0.2 0.6 0.8 0.4 0.4 0.2

TMV 4 0.2 0.4 0.4 0.8 0.4 0.4 0.4

CD (p=0.05) NS NS NS NS NS NS NS

Values mean of five replications NS – Non significant