Root-knot nematodes (Meloidogyne spp.) are recognized as an important group of plant parasitic nematodes worldwide and a major group of plant pathogen in reducing agriculture yield of vegetables. In Pakistan root-knot nematodes are also causing sizeable reduction in yield and quality of the agricultural crops especially underground vegetables. The present research study aims to provide the detailed information that is generated on nematode association with underground vegetables and their diversity in different vegetables (radish, turnip, carrot and sugar beet) of Sindh, Punjab and Khyber Pakhtunkhwa (KP) provinces of Pakistan. Moreover, the impact of root-knot nematode infestation on nutritional quality of underground vegetables radish (Raphanus sativus L.), turnip (Brassica rapa L.), carrot (Daucus carota L.) and sugar beet (Beta vulgaris L.) was also evaluated. In this regard, random surveys were conducted during 2013-2014 and about 600 soil and root samples were collected from underground vegetables (radish, turnip, carrot and sugar beet) to detect the prevalence of plant parasitic nematodes from Sindh, Punjab and Khyber Pakhtunkhwa provinces of Pakistan. A total of 250 samples collected from 14 localities of Punjab, 150 samples from 7 localities of Sindh and 200 samples from 5 localities of KP, Province. Root-knot nematodes, Meloidogyne spp. were frequently recovered from the surveyed areas along with other plant parasitic and free-living soil nematodes. However, it is also evident from this study that these nematodes were found in varied frequency of occurrence in all provinces. From the soil sample analysis forty four nematode species were encountered that were identified morphologically and taxonomically up to species level. These nematodes belong to thirty four genera and twenty three nematode species belonging to the eight different orders in varied frequencies viz., order Tylenchida (54.5%), followed by the order Dorylaimida (20.4 %), Aphelenchida (11.3%), Mononchida (4.5%) and least but equal frequencies were of the orders Enoplida, Triplonchida, Monhysterida and Plectida i.e. (2.1%). Regarding the percentage occurrence of nematode species the overall occurrence of plant parasitic nematodes (76%) was three fold as compared to soil nematodes (24%) in Sindh province during present study.More or less same ratio of occurrence between parasitic nematodes (77%) and soil nematodes (23%) was found in Punjab region where as in Khyber Pakhtunkhwa the parasitic nematodes were encountered in greater percentage (83%) as compared to soil nematodes (17%). Moreover, during the present investigations twenty seven plant parasitic nematodes have been reported as new host records of four underground vegetables from Pakistan. In due course of detailed taxonomic studies, three new nematode species viz., Aphelenchoides turnipi Israr, Shahina and Nasira, 2017; Paradorylaimus dorsocaudali Nasira, Israr and Shahina, 2017 and Tylenchorhyncus carroti n. sp. have been described and illustrated while four new records viz., Amplimerlinius globigerus Siddiqi, 1979; Aphelenchoides siddiqii Fortuner, 1970; Plectus (Ceratoplectus) armatus (Butschili, 1873) Andrassy, 1984 and Tylenchorhynchus usmanensis Khurma and Mahajan, 1987 were also reported during the research period. Furthermore, during the present investigation the nutritional quality of underground vegetables infected by root-knot nematode (Meloidogyne incognita) was also evaluated. It was observed that physiological and biochemical changes occurred due to the invasion of root-knot nematodes in these studied vegetables. Results show that there was a significant difference in root-knot development and reproduction in infected and un-infected host plants. Data indicates that highest reproduction rate and root-knot index was observed in vegetable plants infected with root-knot nematodes after three months as compared to un-infected (control). The physiological parameters as well as biochemical contents showed significant difference in different growth criteria and amount of nutrients between infected host plants as compared to un-infected plants (control). Growth parameters of studied vegetable plants viz., fresh and dry weight and water content were decreased by the infection of root-knot nematode as compared to un-infected (control) plants. Similarly root-knot nematode decreased the host nutrients contents viz., total carbohydrates, total soluble sugars, total protein, total phenols and amino acids. Chlorophyll a, chlorophyll b and carotenoids also decreased in nematode infected plants as compared to control. The investigations and information generated during this period are furnished herein. This study gave the fair report towards biodiversity and nutritional quality because no significant work has been done so far on this aspect in Pakistan.