Survey, distribution and mapping of maize cyst nematode Heterodera zeae in Karnataka

Introduction

Maize (Zea mays L.) is an annual C 4 plant belonging to the tribe Maydeae, of Poaceae family and globally, it is known as "Queen of Cereals" or "Miracle crop" because it has the highest genetic yield potential among the cereals (Binoy Chhetri, 2016). Among all the cereals, maize crop ranks next to wheat and rice in the world as well as in India, in terms of area contributing about 20 per cent share of world total cereal production. In India, it is Hence, the present study was focused on survey, occurrence, distribution, mapping, and identification of maize plant parasitic nematodes in different agro-climatic regions of Karnataka. Therefore, to fill this gap of knowledge and aforesaid reasons, present investigation was carried out with the objective of Survey, distribution, mapping and identification of plant parasitic nematodes in maize different agro-climatic regions of Karnataka.

Material and Methods

Collection of samples

Roving survey was conducted during 2017-18 and 2018-19 in major maize growing districts of Karnataka namely, Bagalkot, Chitradurga, Chickmagaluru, Chamarajanagar, Davanagere, Dharwad, Haveri, Hassan, Mandya, Mysore, Raichur, Shivamogga and Tumakuru, in each district, three taluks were selected and in each taluk, two to five villages were surveyed. While surveying, the following parameters were recorded such as, GIS/GPS information (Latitude and Longitude), soil types, cropping system, weed hosts, other pest and diseases etc., were also recorded along with the samples. During the survey, nematode-infested maize fields were visited. The soil and root samples from five spots were collected randomly with the aid of shovel in the rhizosphere with proper labeling, and several sub-samples were drawn from each of the surveyed areas. The drawn samples were mixed together to make a composite bulk sample of at least one kg of soil and kept in a properly labeled polythene bag. These samples were preserved under the refrigerated condition and analysed for the population of the cyst and other plant parasitic nematodes and the same were maintained under glasshouse condition for further studies. Based on incidence and nematode population, the distribution maps were developed by using GPS/GIS information.

Results and Discussion

Survey and distribution

A systematic roving survey was undertaken during 2017-18 and 2018-19 to determine the occurrence and distribution of maize plant parasitic nematodes in different districts of Karnatakaviz., Bagalkot, Chitradurga, Chickmagaluru, Chamarajanagara, Davanagere, Dharwad, Haveri, Hassan, Mandya, Mysore, Raichur, Shivamogga, and Tumakuru. Total of eightysix samples were collected from maize fields. Samples collected were brought to the laboratory and kept in refrigerator till processing. The samples were processed by using Cobb's sieving and decanting technique followed by modified Baermann's funnel technique and examined under a stereoscopic binocular microscope for the presence of maize cyst nematode H. zeae, Trichodorus and Tylenchorhynchus. The observations recorded such as latitude-longitude, crop age, number of cysts per root system, genotypes, soil type, cropping system and nematode population per 100 cc of soil and other diseases and pests observed during the survey are presented in Table 1 and

Distribution

The maize cyst nematode, H. zeae was distributed in all the surveyed districts of Karnataka viz., Bagalkot, Chitradurga, Chickmagaluru, Chamarajanagar, Davanagere, Dharwad, Haveri, Hassan, Mandya, Mysore, Raichur, Shivamogga and Tumakuru (Fig. 1).

Soil types

With respect to soil types, sandy, sandy loamy, red sandy, red soil, recorded the highest number of H. zeae infestation followed by Trichodorous and also complex infestation of nematodes were also observed from Chitradurga, Shivamogga, Chickmangalur, Hassan, Mandya, Tumakuru and Davanagere district. It is indicated that sandy, sandy loamy, red, red laterite and red sandy soil supported the maximum nematode infection and cyst formation as compared to black soil. This might be due to increased pore space in soil, better aeration and available oxygen in light soils, which increased the nematode movement and reproduction. Light soils favoured higher multiplication of all the nematode species. Similar findings were reported by Rathore et al. (2007) observed that, cyst formation was more in sandy soil as compared to loamy sandy and sandy loam soil and maximum reproduction (RF-4.76 and 5.67) of H. zeae and poor plant growth in light soil whereas, minimum reproduction (RF -2.39 and 2.77) and better plant growth was noted in heavy soil.

Cropping system

Severity of the disease was varying in different cropping systems. Mono-cropping system recorded the highest nematode (J 2 ) infestation compared to the mixed cropping system. In mixed cropping system viz., coconut + coconut in Karehalli (Trichodorus 235.25 / 200 cc soil), Nagashetahalli (Trichodorus and Tylenchorhynchus of 123.25 and 233.50, respectively), Moodalahippe (no nematodes were noticed) and in Chatradalli recorded all three nematodes, i.e., H. zeae, Trichodorus and Tylenchorhynchus, 578.50, 315.50, and 259.00/200 cc soil, respectively. In maize+ arecanut cropping system both Trichodorus and Tylenchorhynchus 200 cc soil, was recorded in Benakaanahalli (178.00 and 144.50, 345.50), Sasvehalli (289.75, and 256.75) and Machagondanahalli (289.50), respectively. Goravarahatti (H. zeae, 799.50 /200 cc soil). And no nematodes were noticed in Nantur village. Maize+methi, maize + pigeon pea and maize + rubber cropping system was noticed in Mokanahalli village of Arasikere taluk of Hassan district, Devagondanakatti village of Ranebennur taluk of Haveri district and Balur village of Hosnagara taluk of Shivamogga district where no nematodes were observed. Out of 86 samples collected, mixed cropping system (11.63%) was noticed in 10 villages and remaining was monocropping (88.37%) in76 villages which showed maximum nematode infection of all the three nematodes compared to the mixed cropping system. H. zeae was noticed in weed (Digitaria sangunalis) in maize fields, especially in Shivamogga and Chitradurga districts which, helps in survival of inoculum throughout the year by acting as a collateral host and enhancement of H. zeae infection in maize (Plate 2a). Continuous monocropping, improper cultural operations, spacing, soil type, temperature, climate change, latitude and longitude also play an important role in the enhancement of nematode infestation in maize in Karnataka. Table 2 and plate 2

Number of cysts per root system

Maximum mean cysts per root system (74.67) were noticed in Chitradurga and this was followed by Dharwad (33.00), Davanagere (28.43), Tumakuru (25.40) and Bagalkot (24.17). And the least mean value was noticed in Mysore (7.20). Table 2 Nematode population per 200 cc soil Maximum mean nematode (J 2 ) population (756.84) of H. zeaeper 200 cc soil was recorded in Chitradurga followed by Dharwad (386.38), Davanagere (316.50), Raichur (262.25) and Bagalkot (261.54). And the least district mean value was recorded in Mysore (88.55). Out of 13 districts surveyed, Trichodorus and Tylenchorhynchus were noticed in seven and five districts, respectively. For Trichodorus, the highest mean value was noticed in Chickmagaluru (265.54) district followed by Davanagere (240.29) district and least was in Haveri (67.09) district. The highest mean value for Tylenchorhynchus was recorded in Chitradurga (256.04) district followed by Davanagere (227.39) district, and the least nematode population was observed in Hassan (117.65) district. Among all the three nematodes noticed, the maximum mean value was recorded for H. zeae (756.84) in Chitradurga district which was followed by Trichodorus in Chikmangalur (265.54) district and least was Tylenchorhynchus population (256.04) in Chitradurga district. Maximum number of cysts per root system and nematode population (J 2 ) per 200 cc of soil was recorded from Haralahalli, Katihalli, Isuru, Siddapura, Chi-kadakatte and Goravarahatti villages which were considered as 'hot spots' of H. zeae. Where in which mono-cropping was followed, and proper sanitation measures were not taken, which lead to an outbreak of nematodes in maize. The disease incidence was varied from locality to locality, because of cropping pattern, environmental conditions, soil type, soil moisture, soil temperature and buildup of inoculum. The higher disease incidence may be attributed to the previous crop, complex nature of cyst with other nematodes and diseases of maize and continuous monocropping system, which might have aggravated the nematode infestation. The results are in conformity with the findings of Similarly, Mehta et al. (2017) [4] during July-September, 2012 in maize growing areas of Rajasthan for maize cyst nematode reported that out of 133 samples collected, H. zeae was recorded in 63 samples with 47.36 per cent occurrence. The highest occurrence was observed from Jhalawar (58.33%) followed by Kota (50.00%) and Baran (34.04%) districts of Rajasthan. On an average, 2.32 cysts per 5g root, 3.58 cyst per 200 cc soil and 147.65 juveniles per 200 cc soil were observed.

District mean of nematode population

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