عنوان مقاله [English]
The deterioration of genetic resources of many field crops due to monoculture and other agricultural activities has been well documented. Estimates indicate that the introduction of new varieties has contributed at least 80% of the increase in crop production, yet, these gains have been offset by the loss of 90% of landraces. The importance of biodiversity in enhancing the sustainability of crop production in agroecosystems has been well acknowledged in the literature. This has been achieved by increasing the biodiversity at cropping systems, species, and variety levels, which corresponds to biodiversity at the ecosystem, species, and ecotype levels in natural ecosystems.
Conservation of biodiversity is prerequisite for sustainable agroecosystems. In the past, diverse species, genotypes and varieties were used in agroecosystems that ensured their sustainability. At present, this approach has changed and new varieties have replaced old ones and on sustainability of systems has been negatively impacted. In the other word, agrobiodiversity or the variety of species in cropping systems has dropped rapidly.
Materials and methods
In this research, agrobiodiversity of melon (Cucumis.melo var. Inodorus), watermelon (Citrullus Vulgaris) and cantaloupe (Cucumis.melo var. Cantaloupensis) were evaluated at the genotype and variety levels. For this purpose necessary data including the number of cultivated genotypes or land races and cultivated area for each of them were collected from 25 counties of Khorasan Razavi province. Accurate data was gathered from the appropriate database and also by filling questionnaire for growing season of 2010-2011. Then spatial biodiversity indices of Simpson and Shannon, evenness, and similarity indices of Sorenson were calculated for three cucurbit crops.
Results and discussion
The results showed that from total cultivated area of cucurbit species in 2010-2011 growing season, 48, 30, 20 and 2 percent belonged to melon, nut watermelon, watermelon and cantaloupe, respectively. Torbat–Jam and Taybad have the greatest acreage of melon in the province with 20 and 24 percent of total cultivated area under these crops. Shannon indices for melon in two counties were 0.06 and 0.22, respectively. However, these counties had the lowest evenness index (0.01 and 0.02). This is a good indication of expanding monoculture and low agrobiodiversity for cucurbit crops in the province. As opposed to the highest evenness index with the value of 0.34 and 0.19 were observed in Gonabad and Sabzevar counties individually. On the basis of the obtained results, by 70 percent of the nut watermelon products was achieved by Juponi landrace mass, which is a reason for the very low genetic diversity of nut watermelon. Due to the reason given above any records was registered for spatial biodiversity indices such as Simpson, Shannon and evenness and similarity indices for nut watermelon landrace masses. The same as nut watermelon, cantaloupe species also was showed low agrobiodiversity in Khorasan Razavi province.
The results of this study indicated that spatial diversity indices for three cucurbit species was not favorable in Khorasan Razavi province. Increasing cultivation area has led to a decline in agrobiodiversity of cucurbit cropping systems. Also, the results showed that Khatoni was the dominant genotype in the melon cultivation area of Khorasan Razavi province. For this reason, melon fruit flies dramatically spread in melon cropping systems of Torbat –Jam and Taybad. So, it is strongly emphasizes that for development and increasing agrobiodiversity in cucurbit cropping system diverse varieties must be used.