Vikas Pareek and Rashmi Varma

INTRODUCTION

Fusarium solani is widely found most important soil borne as well as seed borne pathogen causes various diseases such as root rot, wilt, damping off in veg- etables, legumes, oilseeds and ornamental crops and causes severe losses to economic, medicinal and indus- trial value of the crop (Richardson, 1990; Sultana and Ghaffar, 2007; Abu-Taleb et al., 2011; Khair et al., 2011; Bahar and Shahab, 2012; Karima and Nadia, 2012; Hafizi et al., 2013).

Cluster bean is a highly commercial, industrial and medicinal important leguminous crop due to pres- ence of glactomannan gum in endosperm of seeds. It is highly adapted to arid and semi arid regions of the world requiring low inputs and care. It is cultivated mainly in rainy season as a rainfed crop in arid zones of India and various other parts of the world (Pathak et al., 2010; Pachundkar et al., 2013). Pods and seeds of Cyamopsis tetragonoloba are a very useful local source of fibers. Guar gum extracted from seeds is used as an appetite depressant and also used as a bulking agent in laxative, in gastric ulcer and asthama treatment. It also reduced blood cholesterol and glucose levels sig- nificantly by using an aqueous extract of pods of the plant at a dose of 250mg/kg of body weight (Sharma et al., 2011).

Fusarium solani is serious pathogen which causes wilt, root rot and damping off in cluster bean (Saty- aprasad and Ramaroa, 1981; Dwivedi, Dubey and Dwivedi, 1991). The pathogen is seed borne and trans- mitted in all plant parts of cluster bean (Mathur and Shekhawat, 1988; Dwivedi, Dubey and Dwivedi, 1991). The heavy infection of pathogen causes severe losses in quality and yield of crop which reduce the medicinal and industrial value of the crop.

There is very little information on the seed borne nature of Fusarium solani in guar seeds. Therefore, the objectives of this study were to (i) isolate and iden- tify the seed borne nature of Fusarium solani in clus- ter bean by using incubation tests (ii) to determine the exact location and extent of penetration of seed borne pathogen (iii) to illustrate the disease transmission of the pathogen from seed to seedling/ plant parts. Thus, the present study has significant role to understand the seed borne nature and severity of infection of the pathogen in cluster bean crop which is very useful in obtaining dis- ease free seeds and the wide application of cluster bean seeds in traditional medicine, pharmaceutical, cosmetics, paper industries, textile, bakery and oil field expressed the high commercial values and future perspectives of present research work to increase the profitability and the quality production.

MATERIALS AND METHODS

One hundred twenty seeds samples of cluster bean col- lected from 11 districts of Rajasthan in the year 2011- 2014 were subjected for dry seed examination and incubation tests by Standard blotter method and Potato Dextrose Agar method as recommended by ISTA (Anon- ymous, 1985). In dry seed examination test besides nor- mal looking asymptomatic seeds of various discoloura- tions viz. seeds with black streaks; grey colour seeds with white mycelial growth; shriveled seeds; broken and insect damaged seeds and debris and inert matter were observed. Seeds were incubated on moistened blotters both untreated and 0.5% chlorine pretreated for 2 min in PDA test. Pretreated seeds were spaced (20 seeds/ plate) on petriplate containing PDA medium. Out of these two samples CB29 (Jaipur) and CB70 (Sikar) were used for seed health testing and transmission studies. Disease transmission from seed to seedling/ plant was studied by using asymptomatic and categorized symptomatic seeds (weakly, moderately and heavily). 100 seeds per category per sample were sown in petriplate (20 seeds/ plate) and 50 seeds per category per samples were sown in water agar seedling symptom test (1 seed / test tube) (Khare et al., 1977) and in earthen pots (5 seeds/ pot).

RESULTS AND DISCUSSION

In dry seed examination seeds infected with Fusarium solani showed white mycelial growth on seeds in 43 (0.25-40.5%) seed samples (Fig. 2-A). On incubation the fungus was isolated from 57 (0.25-62%), 53 (0.25-35%) and 15 (0.25-30%) in untreated, pretreated in SBM and PDA respectively. The incidence was high in untreated seeds in SBM. Histogram gives the comparative account of percentage incidence of pathogen on 8th day of incu- bation in both CB29 (Jaipur) and CB70 (Sikar) seed sam- ples (Fig. 1). Highest infection of Fusarium solani in both the samples was obtained in untreated seeds in SBM. Seed germination as well as incidence of pathogen was very low in both pretreated seeds and PDA. In stand- ard blotter test germination varied from 94% to 97% in asymptomatic seeds of cluster bean whereas in weakly moderately and heavily infected seeds it was 25-35%, 18-30% and 7-22%. In water agar test the percentage germination was almost similar except asymptomatic seeds. In asymptomatic seeds the pathogen suppresses the germination after radicle emergence and expressed yellow brown to black discoloration (Fig 2-B). Konde et al. (1980) used blotter paper and agar plate method for isolation of fungal species. Bhatia (1995) have reported reduction in germination by seed borne inoculums of

Fusarium oxysporum. Shakir & Mirza (1992) have also reported F. solani caused significant reduction in seed germination in bottle gourd and sponge gourd (Sha- kir et al., 1995). In Pots the germination varied from 93-96% in asymptomatic seeds and 69-73%, 46-57% and 18-25% in categorized symptomatic seeds (weakly, moderately and heavily) of cluster bean. Survival and vigour of seedling was observed lower in symptomatic seed than the asymptomatic seeds. The pre and post emergence loss in symptomatic seeds was observed very higher than the asymptomatic seeds.

Symptomatic seeds showed initial symptoms on tran- sition zone in the form of pale to brown patches on 3rd to 5th day but in asymptomatic seeds delayed symptoms were observed. Later the symptoms increased rapidly and spread to the cotyledons in the form of irregular necrotic brown colored spots. The severe infection of fungus caused seedling mortality after 15th days. The surviving plants which grew to their full height showed black patches in the form of streaks on basal part of stem near the collar region (Fig 2-C). 30 to 40 days old seedling showed complete yellowing and wilting. Split half of the infected stem showed brown to black discol- ouration and on incubation these halves expressed fun- gal mycelial bits in cortex region (Fig 2-E). The infected plant leaves showed yellowish brown necrotic patches on their surface followed by their shrivelling and droop- ing (Fig. 2-D). On incubation heavily infected leaves showed the presence of fungal spores. The infected pods having less number of seeds than healthy ones. Split half of infected pods showed brown-black patches on outer and inner surface and white colored fungal growth also appeared on harvested seeds (Fig 2-F). Satyaprasad and Ramarao, (1981) reported yellowing and drooping of leaves and black lesions at soil surface of root of guar in F. solani infected plant. The pathogen was isolated from cotyledonary leaves of seedling and plant parts. Cleared and hand cut sections of these seedling and plant parts expressed the fungal mycelium in epidermis, cortex and vascular regions. In present study hilar region of the seed showed aggregation of fungal mycelium. This study suggests that the hilar region is the entry point of fun- gal mycelium. Gupta, Dubey and Singh, (2011) reported high pre and post emergence losses in Dalbergia sisso infected with Fusarium semitectum causing wilt disease. They also reported symptoms of wilt disease as necrotic spots on cotyledonary leaves and browning of radicle. Later these spots were turned into wilting of seedling/ plant and succumb to death. They also revealed trans- mission of pathogen from seed to seedling/ plant.

The guar is commonly susceptible to Fusarium solani causing wilt diseases during summer to rainy season when the conditions are favorable for the growth of fungi (Kamal and Khan, 1967). Dwivedi et al., (1991) reported

Vikas Pareek and Rashmi Varma

that Fusarium solani infected seeds may be symptomatic or asymptomatic. In case of asymptomatic seeds or weakly infected seeds pathogen colonized the seed coat while in case of moderately and heavily infected seeds pathogen colonized to endosperm and embryo of seeds. The seed borne inoculum of Fusarium solani (Mart.) Sacc. deeply present in embryo later spreads rapidly and cause failure of seed germination while in asymptomatic and weakly infected seeds it is transmitted to developing plants. Varma et al., (1989) revealed the colonization of Rhizoctonia bataticola pathogen in all components of moth bean seeds.

Varma et al., (1992) reported seed borne nature of Colletotrichum damatium in Vigna aconitifolia. Varma, (2002) reported Rhizoctonia baticola as a serious patho- gen in the seeds of Vigna aconitifolia crop. The initial symptoms on transition zone as brown black patches on 3rd to 4th day in symptomatic moth bean seeds infected with Rhizoctonia bataticola (Varma, 2003).

Rajput et al., (2010) revealed that maximum infec- tion of frequency exhibited by Fusarium solani colo- nizing stem tissue of Shisham trees followed by bark tissues from seeds and roots. The colonization percent of Fusarium solani was highest as compared to other isolated fungi. Maximum reduction in seed germination was also reported by Fusarium solani. Sadda and Varma, (2010) reported small water soaked or yellowish spots on above ground parts viz. leaves and stem of smooth gourd infected with Colletotrichum orbiculare caused Anthracnose disease.

Farrag and Moharam, (2012) reported transmission of pathogenic fungi of cucumber seeds viz. Fusarium oxysporum, F. solani and Rhizoctonia solani from the germinated seeds to seedling causing pre and post emer- gence death. The transmission rate of tested fungi caus- ing seed rot or pre emergence death was higher than the seedling mortality. Similar observations were reported in tomato seeds (Askar et al., 2014) and in chickpea seeds (Zaidi and Pathak, 2013). Seed-borne fungi are of con- siderable importance due to their influence on the over- all health, germination and final crop stand in the field. The infected seeds may fail to germinate, or transmit disease from seed to seedling and/or from seedling to growing plant (Islam and Borthakur, 2012).

Singh, (2013) reported seed borne nature of Fusarium oxysporum caused wilt disease in lentil and reported pale yellow discolouration on hypocotyl. Later this dis- colouration spreads rapidly on shoot than the primary root region. Ramadan and Zrary, (2014) reported signifi- cant increase in the effect of six fungal pathogens viz. Aspergillus candidus, A. niger, A. sulphurous, Cladospo- rium herbarium, Curvularia lunata, Drechslera tetram- era and Penicillium sp. on pre-emergence damping-off seedlings with soil infestation. Sharma and Sharma

(2014) revealed that the seed borne inoculum of Ral- stonia solanacearum caused pre- and post-emergence losses in brinjal seeds and the symptoms appears as browning of radicle, plumule later turned into necrotic spots with bacterial oozing. Similar symptoms on seeds were reported earlier in tomato (Sharma and Agarwal, 2010) and in cluster bean (Jain and Agarwal, 2011).

CONCLUSIONS

The results suggest that Fusarium solani is most domi- nant pathogen of cluster bean which caused wilt dis- ease and revealed highest infection in untreated seeds in standard Blotter Method. The pre and post emergence loss in symptomatic seeds was observed higher than the asymptomatic seeds. The present study clearly indi- cates the seed borne nature of Fusarium solani and its transmission and pathogenicity from seed to seedling/ plant parts. It also suggests that the pathogen affect all the plant parts and cause severe losses to quality and yield of cluster bean crop. Seed borne inoculum of F. solani was occurs in both asymptomatic and sympto- matic seeds of both the samples. In the asymptomatic seeds the incidence remains low and infection confined to seed coat whereas in symptomatic seeds the infection is intra-embryonal, deep seated and distributed in all the seed components and transmitted to all plant parts viz. root, stem, leaves and pods. The deep infection is difficult to inactive using normal conventional methods of control. Thus, the present study revealed the severity of infection of wilt disease caused by Fusarium solani in cluster bean crop which is useful to obtain disease free seeds of important cash crop and cluster bean seeds have larger future perspectives in terms of higher economic, industrial and medicinal value of the crop than the other legume crops due to presence of glactomannan gum in endosperm of their seeds.

ACKNOWLEDGEMENT

The authors Pareek V and Varma R wish to thank Depart- ment of Science and Technology, Jaipur for financial assistance.

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