They affect the above ground parts, e.g.: leaf, stem and pod anthracnose.
Lesions on stems and pods more clearly defined than those on leaves, grey or brown, slightly sunken with raised dark brown or reddish edge. All vegetative parts, except pulvini, are susceptible during early stages of development; invasion of the tap root of a young plant can lead to death. Elongated dark-brown or black sunken spots with reddish or yellowish margins appear on veins, petioles, stem and pods. Diseased seeds carry the fungus from season to season. Spots on the hypocotyl cause death of the plant. Seedlings show canker on cotyledons. These lesions produce pinkish spore masses during moist weather.
Management:
To control anthracnose, the recommended measures are:
Sowing disease-free seed, crop rotation and field sanitation. Treat seeds for half an hour in 0.125% solution of ceresan or 1% oraganomercurial fungicide (Seedex). Dust seedex or captan at 3 g per kg of seed. Additionally, spray Bordeaux mixture 5:5:50 or a copper fungicide at 1 kg in 250 litres of water as soon as the symptoms appear.
Lablab bean is affected mostly by Leveillula taurica var. macrospora. White floury patches are formed on both sides of the leaves and all portions of the above ground parts, which gradually turn brown. The leaves become yellow and die, while fruits either do not set or remain small. It is a seed borne as well as a soil-borne disease and causes serious damage in the dry weather.
Red and black pustules appear on the lower surface of the leaves. Attacked leaves turn yellow and drop off.
The aphid species, viz., Myzus persicae Sulz., Aphis gossypii G. and Aphis craccivora K. did not transmit the virus. The host range of the virus was found to be fairly wide and it infected plants belonging to the families Leguminosae, Cucurbitaceae, Compositae, Solanaceae, Amarantaceae, Chenopodiaceae and Commelinaceae. The dilution end point of the virus was found to be between 1:100 to1:1000 and thermal inactivation point between 40°C–50°C. The stability of the virus was found to be low and it loses its infectivity after four hours of storage at room temperature 21°C- 28°C. The virus was found to vary considerably from the other ring spot viruses in its mode of transmission, physical properties and host range. Hence, the virus is considered to be different and reported as a new record in India. Affected leaves turn yellowish green, wrinkled and stiff. Though it rarely kills the plants, the growth is retarded and vines do not bear fruits or deformed pods.
Management:
They cause severe growth retardation and characteristic root galls. The symptoms include stunting, loss of yield, reduction in quality of pods; severe deficiency symptoms of some elements, incipient wilting during hot periods of the day, increased susceptibility of foliage diseases of vascular wilts.
The dark green water–soaked lesions may appear on any of the above ground parts of infected plants. They enlarge and coalesce if humidity is high. Older lesions are brown and papery, especially on the pods. In badly infected pods the seed may be covered with bacterial slime, and the organisms may penetrate the seed by way of the funicle and micropyle (7:214).
The bacteria (Pseudomonas pisi) are carried and may over winter on and within the seed, where they remain viable for at least 10 months. The pattern of local spread suggests that the organism travels in drainage water. Water droplets on plant surfaces probably also play a part, as infection takes place through both wounds and stomata.
The virus was found to be sap–transmissible. The aphid species, viz., Myzus persicae Sulz., Aphis gossypii G. and Aphis craccivora K. did not transmit the virus. The host range of the virus was found to be fairly wide and it infected plants belonging to the families Leguminosae, Cucurbitaceae, Compositae, Solanaceae, Amarantaceae, Chenopodiaceae and Commelinaceae. The dilution end point of the virus was found to be between 1:100 to1:1000 and thermal inactivation point between 40°C–50°C. The stability of the virus was found to be low and it loses its infectivity after four hours of storage at room temperature 21°C – 28°C. The virus has been compared and discussed with the ring spot viruses reported from other countries. The virus was found to vary considerably from the other ring spot viruses in its mode of transmission, physical properties and host range.Hence, the virus is considered to be different and reported as a new record in India.
Lablab plants inoculated with Pythium species and Fusarium species separately also developed the wilting symptoms. Another interesting observation noticed was young Lablab plants of 10, 30 and 45 days of age were not infected by these fungi and matured plants of more than 90 days in the flowering and pod setting stage alone were vulnerable to this disease.
The fungal species involved in this study were identified as Pythium middletonii Sparrow., P. aphanidermatum (Edson) Fitzpatrick and Fusarium solani (Mart) Sacc. These fungi were reported to cause stunting and severe wilting of peas 6 weeks after sowing. But these two in combination caused rotting of the cortex tissue in the collar region and wilting. However, no stunting symptom was observed.
The length and fresh weight of shoot and root of D. lablab var. lignosus decreased as the inoculum density of M. incognita was increased from 10–10,000 larvae per 500 cc soil. Significant reduction in plant growth occurred at the 100 nematode inoculum level and final nematode population was greatest at the 100 level. Of 18 lines of D. lablab evaluated for resistance in pot experiments: ILO–28, ILO–29, ILO–33 and ILO–1949–I were resistant. ILO–26, ILO–30 and ILO–1949–III were moderately resistant, while the rest were susceptible.
Similar symptoms have been reported from Pune and whitefly, Bemisia tabaci Genn, has been established as a vector of the disease agent. This paper, however, contains the information on the transmission of the disease agent and type of particles associated with the disease. For whitefly transmission, the method detailed earlier was used for acquisition access feeding (AAF) and inoculation access feeding (IAF). The whiteflies were allowed AAF of 24 h followed by an IAF of 96 h. Tests were carried out by using D. lablab both as donor and recipient host. Twenty to twentyfive whiteflies were used per test plant. Insects were killed by spraying an insecticide after IAF and plants were transferred to insect-proof glass house for 5–7 weeks after inoculation in the manner described earlier.
D. lablab plants showing typical yellow mosaic symptoms were harvested 4 weeks after inoculation with whiteflies and homogenized with 0.1 M phosphate buffer, pH8.0 containing 1% 2–mercaptoethanol and 0.01M radiumethylene–diaminetetraacetate (1:3). The extract was squeezed through cheesecloth, clarified at 8,000 rpm per 20 mt and 4% polyethylene glycol (PEG) and 1.5 % sodium chloride were added. The mixture was incubated at 4°C for 3 h and centrifuged at 10,000 rpm for 20 mt. The pellets were suspended in 0.01 M phosphate buffer, pH 7.5. The suspension was clarified at 8,000 rpm per mt., stirred with 2.5% Triton x -100 for 1 h at 4°C, and centrifuged at 35,000 rpm for 2 h in a Beckman Ti 45 rotor. Pellets were suspended in 5 ml PB, centrifuged at low speed (10,000 rpm) for 10 mt and finally at high speed (40,000) for 2h in Beckman SW 50.1 rotor. The pellet was suspended in 2 ml of buffer and subjected to a low speed centrifugation for 10 mt at 8,000 rpm. Linear sucrose gradients (10–40%) were prepared in 0.1 M phosphate buffer, pH 7.0 containing 0.001 M EDTA. The partially purified preparation (0.5 ml) was layered on the gradients and centrifuged at 40,000 rpm for 2.5 h in a Beckman SW 50.1 rotor. Two distinct light scattering bands observed were collected and concentrated by pelleting at 40,000 rpm for 2 h. The samples thus obtained were stained with 2% Uranyl acetate (pH 4.0) and examined under a Philips 410 transmission electron microscope. Particles were measured with a x 7 Bauch and Lamb magnifiers directly from negatives.
Electron microscopy of the sample obtained in the upper band revealed the presence of 12-nm particles, whereas 20 x 40 nm geminate particles were found in the lower band. However, the intact geminate particles were only a few in number (1 or 2 particles per field) but most of the particles appeared to be degraded. The smaller number of geminate particles may be due to their susceptibility to the 2 % Uranyl acetate used for staining, as gemini viruses have been reported to be very susceptible to negative stains. Particles of 12–nm appear to be phytoferritins.
Whiteflies transmitted the disease but at a very low transmission rate (2/50). These findings confirm the earlier report, where only 3% transmission of the disease was achieved by B. tabaci.
The yellow mosaic disease agent exhibits the characteristics shared by some suspected or proven gemini viruses group members including whitefly transmissibility and particle morphology. The gemini viruses may be responsible for the yellow mosaic in Dolichos lablab. However, for unequivocal proof of their involvement in the disease, an extensive investigation is needed.
The most common pathogenesis–related protein in this host–virus combination average kDa in MW and an additional 6 bands (16–24 kDa) were also detected. In the range 24–45 kDa, a further 3 proteins were present in infected samples. Seven proteins were present in both diseased and healthy samples, but their concentrations were much lower in healthy than in diseased tissues.
Reproduction of Meloidogyne javanica on Crotalaria juncea, PI. 207657 and cv. Tropicsun, Sesamum indicum, Dolichos lablab and Elymus glauca was assessed using a root gall index, a reproductive index obtained by dividing the final population of juveniles (J2) in the soil by the initial J2 population (Pf/ Pi), and the number of J2/g of root recovered from roots by mist chamber extraction. Lycopersicon esculentum (cv. Uc. 204C) was included as a susceptible host. The root gall index and soil reproductive index were poor indicators of the host status of our test plants as compared with mist chamber extraction of J2 from roots. Lycopersicon esculentum had a mean root gall index of 7.8. Some plants of S. indicum and E. glaucus had a few galls and other plants had none, with mean root gall indices of 1.6 and 0.8, respectively. No galls were observed in C. juncea and D. Lablab. Lycopersicon esculentum had the highest mean soil Pf/ Pi value (mean=1.93), while in C. juncea and some replicates of S. indicum no soil J2 were found. Even though some replicates had no galls, all replicates supported nematode reproduction. The mean numbers of J2 per gram of root after 5 days of mist extraction were 447.7, 223.3, 165.5, 96.9, 42.3 and 41.9 for D. Lablab, L. esculentum, E. glaucus, S. indicum and C. juncea – PI 207657 and cv. Tropicsun, respectively. Accurate assessment of nematode resistance was influenced by sampling time and the nematode extraction techniques used. Individual plants of both C. juncea and S. indicum supported nematode reproduction to some extent, however, both C. juncea and S. indicum have potential as cover crops to reduce M. javanica numbers.
Ninety nine varieties from Uttar Pradesh were screened for their reaction to Alternaria leaf spot. Cultivars including Arka Vijay, JDL 77, Pusa Early Prolific and Rajani were found to be resistant and Arka Jay, Culture 6802, 7103, HA3, HD1, 81, JDL 85 and Kalyanpur Type 2 were found to be highly susceptible.
Aspergillus flavus is a fungal pathogen of maize causing an important ear rot disease when plants are exposed to drought and heat stress. Associated with the disease is the production of afflatoxins, which are a series of structurally related mycotoxins known to be carcinogenic. Previous research has suggested that the alpha–amylase of A. flavus promotes aflatoxin production in endosperm of infected maize kernels. The report here is about the isolation and characterization of a 36 kDa alpha–amylase inhibitor from Lablab purpureus (AILP). AILP inhibited the alpha–amylases from several fungi but had little effect on those from animal and plant sources. The protein inhibited conidial germination and hypral growth of A. flavus. The amino acid sequence indicated that AILP is similar to lectin member of a lectin–arcelin–alpha–amylase inhibitor family described in common bean and shown to be a component of plant resistance to insect pests. AILP also agglutinated papain–treated red blood cells from humans and rabbit. These data indicate that AILP represents a novel variant in the lectin – arcelin – alpha – amylase inhibitor family of proteins having lectin–like and alpha–amylase inhibitory activity.
Characteristic symptoms of the disease are bright yellow mosaic patches on leaves with significant yield reductions. A sample from the DYMD–affected Dolichos plants was collected from Mysore (Karnataka) in India in February 2004. The putative virus was transmitted by the whitefly, Bemisia tabaci from Dolichos to Dolichos
Total DNA was extracted from the symptomatic leaves and used to PCR- amplify a begomovirus DNA – A Component using degenerate primers (Muniyappa et al., 2003). Sequence generated from this PCR product was used to design virus- specific primers to obtain full length DNA-A clones. The sequence of one clone was determined to be 2760 nucleotides in length and to be most similar to the sequences of DOYMV- (Bangladesh) (AY 271891) and a further clone of DOYMV originating from India (AY 309241) at 95.2% and 93.4% sequence identities, respectively. The number and arrangement of open reading frames on DNA-A were similar to viruses of the genus Begomovirus (family Geminiviridac) originting from the Old World. Attempts to identify DNA-B and –β components by PCR (Muniyappa et al., 2003; Briddon et al., 2002) were unsuccessful.
Phylogenetic analysis shows that the three DOYMV isolates to form a sister clade to the mungbean–infecting begomoviruses which together cluster separately from begomoviruses infecting other hosts in the Indian sub-continent. DOYMV has only 62.9–63.8% identity with mungbean viruses and lower sequence identities with other begomoviruses (61.0–63.9%). These results show that, on the Indian sub-continent, Dolichos is infected by a distinct species of begomovirus.
Experiments were conducted in 2004 and 2005 to evaluate the reaction of Lablab to southern root-knot nematode (Meloidogyne incognita). Lablab breeding lines and the check cultivar “Rongai” were inoculated with southern root-knot nematode, evaluated and compared to Iron and Clay cowpea (Vigna unguiculata) under greenhouse conditions. In 2004, average gall scores (0 to 5 with 5 = severe galling) ranged from 1.3 to 4.7 for Iron and Clay cowpea and T x 41.97 Lablab, respectively. Average nematode egg production ranged from 410 to 33,639 eggs per g of root fresh weight of Iron and Clay cowpea and T x 41-97, respectively. The best Lablab line was T x 35–03 with 2.3 gall score and 6696 eggs per g of root fresh weight. One plant of T x 35–03 was noted with no galling and only 26 eggs per g of root fresh weight. In 2005 revaluation, T x 35–03 was again the best Lablab line with a gall score of 1%. In the 2005 study, “Rongai” had the most severe galling of all the lines evaluated.
Out of ten fungicides and two neem fomulations assayed in vitro against Sclerotinia sclerotiorum (Lib.) de Bary causing stem and pod rot of dolichos bean, vitavax, companion, bavistin, score, mancozeb and thiram proved to be the most effective as they inhibited the growth of fungus completely (100%). Among the partially effective one, zineb gave the highest inhibition (88.80%) followed by neem formulations. Fungicides and neem formulations found effective and partially effective in in-vitro test were further evaluated as foliar spray for the management of disease. Corresponding increase in yield was obtained by application of vitavax followed by companion and bavistin. Neem oil proved to be least effective in reducing the disease incidence and increasing the pod yield.
The disease was most conspicuous by causing typical anthracnose symptoms first appeared as regular to irregular shaped small brown to black spots on leaves and petioles. These spots enlarged, forming irregular patches of dead tissue. The central portion of the diseases spot on leaves become dry and papery in nature, detached and fell off to form a characteristic “shot hole” symptom. On petioles, typical dark black lesions appeared ad elongated brown to black lesions developed which enlarged, coalesced all along the petioles and, caused the sunken and black lesions.
The small black fruiting bodies were observed on infected spots. The conidia of Colletorichum lindemuthianum were hyaline, single celled, oblong, cylindrical with rounded ends or some time with one end slightly pointed. The length and breadth of the conidia ranged from 9.5 -11.5µm x 3.5-4.5 µm. The spore germination on different substrates indicated that maximum spore germination was observed in two per cent sucrose solution (51%) followed by one per cent sucrose solution (35%). The least spore germination was observed in case of distilled water (8%).
Maximum radial growth of fungus was observed on Potato dextrose agar (81.00 mm) followed by Richard’s agar medium (79.00 mm) and brown’s agar (72.32 mm). Least growth was observed on Sach’s agar medium (60.00). the growth of C. lindemuthianum on Potato dextrose agar produce brownish white, uniform, circular, compact mycelium at periphery but raised in centre, regular and fluffy growth with concentric rings were observed. Richard’s agar produce whitish brown, uniform, circular, regular and partially fluffy growth was recorded.
Among the carbon sources tested against C. lindemuthianum, sucrose was found to be the best for the growth (82.67 mm) followed by dextrose (80.00 mm). The least growth was observed in citric acid (37.67 mm). Among the nitrogen sources tested, potassium nitrate was found to be the best source of nitrogen (78.33 mm), followed by ammonium nitrate (69 .00 mm), while growth did not occur at occur in ammonium molybdate.
Maximum mean radial growth was observed at a temperature of 280 C (79.33 mm) followed by 250 C (26.67 mm). The least growth was occurred at 150 C (36.33 mm). The C. lindemuthianum reached maximum growth at pH 6(77.33 mm) followed by pH 7 (75.33 mm).
Among the biocontrol agents, maximum inhibition of fungus was observed in Trichoderma harzianum (73.54%) The least per cent inhibition was observed in Basillus megaterium (39.46%). Out of eight fungicides tested, in vitro Mancozeb inhibited 100 per cent mycelial growth at 400 and 800 ppm, whereas least per cent inhibition was observed in case of copper oxychloride (6.72%) at 100 ppm. Among the systemic fungicides, carbendazim recorded cent per cent (100%) mycelial inhibition at all the concentrations of 50, 100, 200 and 400 ppm. Whereas the least per cent mycelial inhibition was observed in case of hexaconazole (84.87%) at 400 ppm.
Three bioagents (Trichoderma viride, T. harzianum and Gliocladium virens) and five biopesticides (Achook, Neemgold, Wannis, Spictaf and Neemazal) were evaluated under in vitro and in vivo conditions against Colletotrichum lindemuthianum. All the three antagonistic fungi caused significant inhibition of mycelial growth, maximum being with T. viride (69.21%) followed by T. harzianum (64.20%). Among the biopesticides tested at four concentrations, Wanis applied @ 1000 µl/ml caused maximum inhibition of 82.12 per cent followed by Spictaf (52.85%). T. viride and Wanis @ 1000 µl/ml were most effective in reducing the seed borne infection. Integration of bioagents with Bavistin showed that disease can be effectively managed with seed dressing either with Bavistin or biopesticide followed by foliar treatment with fungicide or biopesticide.
Investigations of yield loss assessment under glass house conditions due to anthracnose (Colletotrichum lindemuthianum) infection at different stages of plant growth revealed adverse effect on various growth parameters of highly susceptible kidney bean cultivar Jawala as compared to healthy plants. However, seed borne infection and cotyledonary leaf stage infection caused maximum reduction in almost all the growth traits. Yield of dry bean varieties obtained from plants inoculated at different stages of plant growth revealed that the disease caused significant decrease in yield of both the varieties. Marked differences in terminal disease severity at different stages of plant growth were observed with the maximum severity in pod development stage infection in both the cultivars viz Jawala (27.04%) and Local (16.23%). Considerable eduction in the yield of green pods of both the types of beans viz., Contender and Luxmi was observed when inoculated with pathogen at different stages of plant growth.
Dolichos bean, Lablab purpureusL. (Sweet) is an ancient legume widely grown throughout the world for its vegetable or pulse for human consumption or as animal forage or feed. Anthracnose in dolichos bean caused by Colletotrichum lindemuthianum (Sacc. & Magnus) is the most widespread and destructive disease. The disease is prevalent in Dolichos bean growing areas of Karnataka and is considered as a limiting biotic factor for successful cultivation. In the present study, different cultivars of Dolichos bean were used and an intensive roving survey for anthracnose of Dolichos bean was carried out during kharif 2010 and 2011 in major dolichos bean growing areas of Southern Karnataka to get precise information on the distribution and intensity of the disease. The data on survey revealed that the anthracnose severity varied from locality to locality. The average disease severity varied in various locations in different districts owing to varied agro climatic conditions and also different cultivars used. In Southern Karnataka, the disease severity was found more in Mysore district (45.23%), followed by Chamarajanagar (38.12%) and Mandya (32.59%) and the least in Ramanagaram district with 23.86 per cent.
Dolichos bean is an important pulse-cum-vegetable crop. The crop is affected by many fungal diseases viz., anthracnose, early blight, root and stem rot, powdery mildew and rust. Among them anthracnose is an important disease present throughout the world but severe in tropical and subtropical regions. Bean anthracnose caused by Colletotrichum lindemuthianum.(Saccand Magn.) Scriber affects all plant parts viz., stem, pods and seeds. One hundred and ninety five germplasm lines of dolichos bean were screened under field condition for identification of resistance source to anthracnose. Among the genotypes screened for disease resistance, 9 genotypes viz., GLB3, GLB 4, GLB 8, GLB 9, GLB 11, GLB 19, GLB 60 GLB 166 and GLB 167 were found immune, 48were resistant, 83 were moderately resistant, 51 were moderately susceptible, 4 susceptible, but none of the genotype came under highly susceptible category.
Anthracnose disease of dolichos bean caused by the fungus Colletotrichum lindemuthianum is a serious disease in southern Karnataka where the crop is grown during kharif season. Survey conducted during kharif 2010 and 2011 revealed that the disease was prevalent in all the fields surveyed and the per cent disease severity was found more in Mysore district (47.54%) followed by Chamarajanagar (40.71%) and Chikkaballapur (33.95%) and least in Ramanagar (23.58%). Average pod infection was highest in Mysore district (23.87%) followed by Chamarajanagar district (18.43%) and Chikkaballapur (14.31%) and the least in Ramanagar district (8.44%).
The maximum mycelial weight was observed after 12 days of incubation. Maximum conidial germination (42.54%) was observed on 2% sucrose solution. Solid medium like Richard’s agar, liquid medium like Richard’s medium and Sabourad’s medium, temperature of 280C and pH 6.0 were found best for the growth and sporulation of C lindemuthianum. Sucrose as carbon source and potassium nitrate as nitrogen source were found to be the best for growth and sporulation of the fungus.
Out of 400 genotypes screened against anthracnose under field conditions, four genotypes viz., GL 152, 364, 371 and 388 were found moderately resistant, 28 resistant, 209 moderately susceptible and 159 susceptible to anthracnose. Out of legume crops and ten weed species tested for its host range, only two legumes viz., French bean and horsegram were infected.
In vitro evaluation revealed that, carbendazim and carbendazim + mancozeb and manoczeb were found effective. Among botanicals, neem seed kernel extract (NSKE), onion and ginger significantly inhibited cent per cent mycelial growth. Among bioagents Trichoderma viride inhibited the growth of fungus to the maximum extent (92.22%). In the management study carbendazim was found to be effective in control of the anthracnose with maximum BCR.