F. udum was transmitted by infected seeds of 5 wilt susceptible pigeonpea cultivars collected from diseased susceptible pigeonpea cultivars collected from diseased plants. The fungus was not isolated from the wilt susceptible cultivars ICP 2376 and ICP 8518. Seed treatment with a mixture of benomyl and thiram completely eradicated the pathogen., 7 ref., F. udum was transmitted by infected seeds of 5 wilt susceptible pigeonpea cultivars collected from diseased susceptible pigeonpea cultivars collected from diseased plants. The fungus was not isolated from the wilt susceptible cultivars ICP 2376 and ICP 8518. Seed treatment with a mixture of benomyl and thiram completely eradicated the pathogen

Haware, M P

Kannaiyan, J

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Haware, M .  P. and Kannaiyan. J .  (1992). Seed Sci. & Technol.. 20 ,59741  Seed transmission of Fusarium udum in pigeonpea and its control by seed-treatment fungicides M.P.  H A W A R E  and J .  K A N N A I Y A N  International Crops Research Institute for the Semi-Arid Tropics (ICRISAT). Patanchcru P.O.. Andhra Pradesh 502 324, India (Accepted July 1992) Summary Thc pigeonpea wilt pathogen, Fusuriurn udunr, was transmitted by infected sceds of live wilt susceptible pigeonpea cultivars collected from diseased plants. Thc fungus was not isolated from the wilt susceptible cultivars, ICP 2376 and ICP 8518. Sccd treatment with a mixture of bcnomyl and thiram completely cradi- cated the pathogen. Introduction Wilt of pigeonpea (Cajanus cajun (L.) Millsp.) caused by Fusarium trdum Butler has been reported from India and several other countries (Nene, Sheila and Sharma, 1989). It is a serious disease problem in the Indian subcontinent and eastern Africa (Kan- naiyan, Nene, Reddy, Ryan and Raju, 1984). Seed transmission of the wilt fungus has been reported by some workers (Shukla and Rhargava, 1976; Jeswani and Gemawat, 1981). On the contrary, Mohanty (1946) reported that Fu,suriurn udum was not carried within the seed. The available evidence on the internal seed-borne nature of Fusarium udum is not conclusive. Since we at ICRlSAT are involved in considerable international exchange of pigeonpea seed, we decided to investigate the internal seed- borne nature of the wilt fpngus and control of the seed-borne phase with seed-treat- ment fungicides. Materials and methods Collection of seed Seeds of seven wilt susceptible cultivars (ICP 2376, ICP 851 8, ICP 1903, ICPX 78 148, BDN-1, C-1 I and Hy 3C) grown in a wilt sick plot in 1983- 84and 1985- 86 at lCRlSAT Center, Patancheru, India were collected from plants that wilted prior to maturity and from plants that did not wilt. To avoid contamination during harvesting and threshing, seed was removed from dried pods of individual healthy and wilted plants by hand and air-dried at room temperature. The seed was bulked into 14 lots (seed from healthy and wilted plants of the seven cultivars) and stored in paper bags at 5°C. M. P. H A W A R E  A N D  J .  K A N N A I Y A N  Testing procedures In all the experiments, unless stated otherwise, (i) 400 seeds of each cultivar were used and (ii) seed was surface-sterilized by dipping for two minutes in a 2.5% solution of sodium hypochlorite. The blotter test was used to measure seed germination (ISTA, 1966). Seed was placed in plastic Petri dishes on top of three layers of moistened, sterilised blotters and incubated at 25°C for one week. For detecting Fusarium udum in seed, Nash's medium was used (Nash and Snyder 1962). Nash's medium consists of 1.5% peptone, 0.1 % KH,PO,; 0.5% MgSO,; 7H20; 2% agarand0.75% pentachloro- nitrobenzene. The medium was adjusted to pH 6, autoclaved and 300 mg of streptomy- cin sulphate and 250 mg of neomycin sulphate were added to a litre of medium prior to pouring into Petri dishes. The surface-sterilized seeds were plated on this medium (10 seedlplate) and incubated at 25°C for one week in a cycle of 12 hours of near-UV light followed by 12 hours of darkness. The number of seeds germinated on blotter and number of colonies of Fusarium udum on Nash's medium were recorded. A disease transmission test was also conducted to confirm the transmission of Fusa- rium udum by infected seed. The surface-sterilized seeds were sown in autoclaved, (121 "C for 2 hours) fine riverbed sand in 15 cm diameter plastic pots in a greenhouse. Germination-was recorded 15 days after planting and seedlings were checked for wilt symptoms up to 60 days. Isolations were attempted from wilted plants. Pathogenicity tests Isolations were made on potato dextrose agar (PDA) from plants showing wilting in the disease transmission test. To determine pathogenicity of culture isolates, 10 day-old healthy pigeonpea seedlings of ICP 2376 were root dipped in conidial suspen- sions of the isolates and transplanted into autoclaved riverbed sand in 15 cm pots. To eliminate the chances of seed-borne infection, the seedlings for the pathogenicity test were raised in sterile sand from surface-sterilized seed collected from healthy plants. Seed treatment with fungicides Fungicide formulations used were Benlate 50 W.P.@ (50% henomyl), Bavistin W. P.@ (50% carbendazim), Tecto-60@ (60% thiabendazole), and ThirideB (75% thiram). The fungicidal mixtures tried were 1 : 1 in proportion. Unless stated otherwise the fungicidal dosage was 2.5 g of the commercial formulation per kg of seed. Results Detection of the pathogen on medium Fusarium udum colonies were mostly rosy in colour with felted aerial mycelium. The m&roconidia were 'hook shaped' which enabled easy identification of colonies. Fusa- rium udum was present in the seeds of five susceptible pigeonpea cultivars; viz., ICP 1903, PCPX 78148, BDN-1 (tested over two years) and C-1 l and Hy 3C (tested in 85/86 only). It was not isolated from two other wilt susceptible cultivars ICP 2376 T R A N S M I S S I O N  A N D  C O N T R O L  O F  P I G E O N P E A  W I L T  Table I .  Detection of Fusarium uduni in seeds of 7 healthy and wilted pigeonpea cultivars. Cultivar $ ICP-2376' ICP-85 18* ICP-I903 ICPX 78 148 BDN- I C-l l* Hy 3C* Percentage seed infection Seedling disease transmission on Nash's medium1 (percentage wilt)' A = Seeds from wilted plants. B = Seeds from healthy plants. NT = Not tested. = No. of seeds tested were 400 for cach cultivar. * Note that the data were obtained Tcfr the year 85 X h  only. and ICP 8518 which were tested in one year only (Table 1). These results confirm the seed borne nature of the pigeonpea wilt pathogen. The pathogen was also not isolated from seeds of healthy plants. The pathogenicity of Fusaritmt utium isolates from seed was confirmed. Wilt in a disease transmission test Wilt occurred in those plants of five cultivars which showed seed infection on selective medium. Wilt was not observed in seedlings of ICP 2376 and 85 18. Likewise wilt was absent in the seedlings grown from seeds collected from healthy plants of seven culti- vars (Table I). These results confirm the seed transmission of the fungus in a medium Table 2. Effect of fungicidal seed treatment on sccd-borne Fu.suriurn rrllum. Fungicide Application ratc lnfcction dctcitcd on (g a.i./kg) Nash's medium' (Oh) BDN l Benomyl 1.25 2 Carbendazim 1.25 3 Thiabendazole 1 .SO 4 Thiram 1.875 4 Benomyl + Thiram 0.625 + 0.9375 0 Carbendazim + Thiram 0.625 + 0.9375 2 Check 12 = No. of seeds tested were 400 per fungicide per cultivar. 599 M. P. H A W A R E  A N D  J .  K A N N A I Y A N  Table 3. Effect of benomyl + thiram' (I : 1) seed treatment on seed-borne Fusarium udum Cultivar Percentage germination Percentage infection Nash's medium In sand3 A B A B ' Fungicide at 2.5 g/kg ofcommercial formulation applied as wet seed treatment. * Blotter test. Plants were observed for wilting up to 60 days after sowing. A Untreated seeds. B Fungicide treated seeds. No. of seeds tested for a cultivar were 400 in each test. of riverbed sand. Fusarium udum was isolated from wilted seedlings and its pathogeni- city was confirmed. Seed treatments with fungicides Fusarium udum was not recovered from seed treated with the mixture of benomyl and thiram on Nash's medium (Table 2). Benomyl or thiram alone and thiabendazole or carbendazim did not eradicate the pathogen from the seed. Benomyl + thiram (I : I) in a commercial formulation (1.25 g benomyl + 1.25 g thiramlkg seed) completely eradicated Fusarium udum from infected seed of BDN-1 and Hy 3C. The effectiveness of the fungicide mixture was again confirmed in a laboratory and glasshouse test, where seedlings were raised from fungicide-treated and untreated seed of two cultiva~s. Wilting was not observed in seedlings grown from fungicide treated seeds (Table 3).  No adverse effect on seed germination from seed treatment was detected. Discussion The results demonstrated that Fusarium udum, the pigeonpea wilt pathogen, infected pigeonpea seeds. A proportion of seeds collected from wilted plants bore the fungus but seeds from healthy plants did not. This was confirmed both on the selective agar medium and in disease transmission tests in riverbed sand in the glasshouse. The possibility of the seed transmission of Fusarium udum was pointed out by Jes- wani and Gemawat (1981) and Shukla and Bhargava (1976). However they failed to obtain clear evidence of internal seed transmission of Fusurium udum. It was not clear from their papers if the seeds they used for those tests were obtained from wilted plants. Fusarium udum can be isolated as a surface contaminant from pigeonpea seed. J,ikt!wise the name of the cultivar from which the seed was obtained was not men- tioned. It is important to know the cultivar, because there may be a clear difference between cultivars with regard to seed infection of the developing seed (Table 1). In TRANSMISSION A N D  CONTROL OF PIGEONPEA WILT limited tests the pathogen did not infect the seeds of two susceptible cultivars of pigeon- pea. Other susceptible cultivars allowed the pathogen to establish in the seed before wilting. ~nfectid seed may be the primary means of spreading Fusarium u h m  over long distance and into new areas where it could become a primary source of inoculum for disease development. Fungicidal treatment of seed may be an important method of preventing or delaying the introduction of Fusarium udum in wilt-free pigeonpea growing areas. A mixture of benomyl and thiram effectively eradicated seedborne Fusarium udum and therefore international movement of pigeonpea seed needed for germplasm exchange should not be affected adversely, provided treated seeds are used, References International Seed Testing Association (ISTA) (1966). International rules for seed testing. Proceedings (?/ International Seed Testing Associalion, 31, 1-1 52. Jeswani, M. D., and Gemawat, P. D. (1981). Seedborne nature of wilt of arhar. Page 162 in Abstract of papers of the Third lnternational Symposium of Plant Pathology, 14-18 December. 1981. New Delhi, India: Indian Phytoparhological Sociery. Kannaiyan, J., Nene, Y. L., Reddy.-M. V., Ryan, J .  G, and Raju, T. N. (1984). Prevalence of pigeonpea diseases and associated crop losses in Asia, Africa and America. Tropical Pesr Mrmagemenf, 30,62 71. Mohanty, U. N. (1946). The wilt disease of pigeonpea with a special reference to the distribution of the causal organism in the host tissue. Indian Journal of Agricultural  science^, 16.379-390. Nash, S. M. and Snyder, W. C. (1962). Quantitative estimations by plate counts of propagules of'the bean root rot Fusarium in field soils. Phyroparhology, 52,567 572. Nene, Y. L., Sheila, V. K. and Sharma, S. B. (1989). A world list of Chickpea (Cicer arietinum L.) and Pigeonpea (Cajanus cujun (L.) Millsp.) Pathogens. Legumes Parhology Progreavs Reporf, 7 ,  1 -  23. Patan- cheru, 502 324, India: ICRISAT. Shukla, D. N. and Bhargava, S. N.  (1976). Some pathogenic fungi from pulses and oil seed crops. Proceed- ings of Narional Academy ofscience, India, 46 ( B ) ,  53 1 532, 

Seed transmission of Fusarium udum in pigeonpea and its control by seed-treatment fungicides

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Seed transmission of Fusarium udum in pigeonpea and its control by seed-treatment fungicides

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