In the present submission, the authors have highlighted the distribution and structure of some of the deleterious PPNs prevailed in a major common variety known as Cherry tomato (Desi) in Jhansi India. The physicochemical properties of soil and its relationship with the abundance of PPN genera have also been explored. The six PPNs genera have been enumerated for the first time in the tomato crop grown in this region. The distribution of six genera of PPNs (Meloidogyne, hoplolaimus, Rotylynchulus, Pratylenchus, helicotylenchus, Criconmea) based on prominence value and the significance test was also verified with morphological analysis.
Site S-3 and S-2 were documented in higher populations of PPNs. The high PPN population in these two areas could be associated with intercropping of tomatoes plants with susceptible crops like – Ginger, Turmeric, Fenugreek, red chili, Bringles, Papaya, Coriander, Carrot, and cabbage spotted during the survey. Different varieties of crops were grown in the previous three years in the same field where tomato plants are cultivated at the present time, explains the occurrence of the high number of nematodes in roots. The previously grown crops provided the infection of tomato plants after planting. Prolonged mono-cropping of susceptible host plants may lead to PPNs build-ups which cause serious crop damage (Bhan, et al. 2010). These areas also receive a substantial amount of rainfall that ensures prolonged moisture in the soil for nematode movement (Waswa et al., 2020). During the survey, it was noticed that site S-1 (Harpura), had a lesser number of total nematodes, this may be the reason that the farmers of that village applied inorganic fertilizer and decomposed cow and buffalo dung, which reduced the total number of nematodes significantly. Organic decomposed manure releases toxic chemical against PPNs and enhances the proliferation of antagonistic micro-organism against PPNs (Waswa et al., 2020). It was observed that infection of PPNs on tomato crops declined significantly during the summer season because hot and dry climatic conditions did not allow them to grow. Tendering support to the above findings, Hussey (1996) stated that hot and arid seasons reduce PPNs infection in crops.
During the investigation, it was ascertained that all three sites of tomato plant cultivation had been predominantly affected by PPN genera Meloidogyne followed by Pratylenchus, Rotylenchulus, and Helicotylenchus. Vasquez and Soria. 2017 examined the similar distribution of PPNs in tomato crops and Meloidogyne spp. was noted as the most abundant genera. These PPNs are polyphagous and their huge number is associated with the plantation of tomato crops with other prone host crops. On the other hand, while preparing the questionnaire, the authors' interacted with crop growers and ferreted out that many of them had grown the crop in the past three years which was highly susceptible to PPNs. This could be the key cause of the high number of PPNs extracted from soil and roots. During the survey, the low population of Hoplolaimus and Criconema genera was observed in cultivated lands. Blake (1969) opined that it could be possible because of the presence of other aggressive dominant genera and interspecific competition from other PPNs such as Meloidogyne. spp., Pratylenchus spp., Rotylenchulus spp., and Helicotylenchus spp.,
Free-living nematodes (FLNs) are a very important group of nematodes that feed on bacteria, algae, dead organisms, and living tissues. They release nutrients for plant use and improve soil structure and water-holding capacity. During the present investigation, the count of FLNs, in all three sites S-1, S-2, and S-3 was quite low as compared to PPNs, similar to the findings of Waswa et. al. 2020. At the crop sites, the farmers were advised to use cow and buffalo dung in the soil because organic amendments (OAs) help in enhancing the FLNs population and combat the population of PPNs as suggested by Hillocks and Waller 1997.
Soil physiochemical parameters play a vital role in the improvement of soil fertility for the cultivation practices of agricultural crops, tomatoes, and have been found to influence the distribution of PPNs in all three sites of study. According to Kandji et al. 2001 and Kimenju et al. 2009, the soil physio-chemical properties regulate the abundance, distribution, and community structure of nematodes. The minimum population of PPNs was recorded in S-1 (Harpura), it might be occurred due to a high level of organic carbon (OC), organic amendments (OAs), and nitrogen (referred to the table-4) in comparison to that of S-2 (Basvan) and S-3 (Chitavar), which were recorded a high number of PPNs. Waswa et al. 2020 stated that Organic carbon (OC) increases the number of antagonistic micro-organisms in the soil which reduce the PPNs. On the other hand, Agbenin (2004) referred that soil organic amendments (OAs) increase the build-up of nematodes trapping fungi compared with inorganic fertilizers. Nchore et al. 2012 have opined that animal manure has been used in the reduction of RKNs and other PPNs, which is suggestive of the organic management of the PPNs population in tomato crops.
The Physico-chemical analysis of soil also revealed that S-2 and S-3 sites had greater phosphorus (P) and potassium (K) levels than S1. Phosphorus and potassium supplement the nutrition, multiplication, and production of eggs in the nematode population. Potassium also improves root growth, extending the root surface area for nematode attack and feeding (Badra and Yousif. 1979). This observation was in agreement with studies by Kandji et al. (2001), Badra and Yousif. 1979and Wasva et al. 2020.
Most of the soils in the study sites were red soil (RS) and black soil (BS). According to Talwanaet al. 2008 above types of soil structures support the high nematode population densities. Such soils are highly porous with good aeration and favour the movement of nematodes (Talwanaet al. 2008. McLean and Lawerence. 2000. Norton and Norton. 1978. Since the survey was conducted during the post-monsoon season (October- December 2021) so all the sites had a copious amount of moisture in the soil which favoured the greater PPN populations. Wallace. 1983 and Jaetzold et al. 2006 also postulated similar that humidity and moisture in soil received due to rainfall create a favourable condition for nematode development. Nysani et al. 2008. stated that pH 4–8 range tolerated by most PPNs, and the present study also revealed that the optimum pH ranged between 7-7.3 which was found conducive for the growth and development of nematodes.