Abstract
Witches’ broom disease has led to major losses in lime and alfalfa production in Oman. This paper identifies bioclimatic variables that contribute to the prediction of distribution of witches’ broom disease in current and future climatic scenarios. It also explores the expansion, reduction, or shift in the climatic niche of the distribution of the disease across the different geographical areas of the entire country (309,501 km²). The maximum entropy model (MaxEnt) and geographical information system were used to investigate the potential suitability of habitats for the phytoplasma disease. This study used current (1970–2000) and future projected climatic scenarios (2021–2040, 2041–2060, 2061–2080, and 2081–2100) to model the distribution of phytoplasma for lime trees and alfalfa in Oman. Bioclimatic variables were downloaded from WorldClim with ± 60 occurrence points for lime trees and alfalfa. The area under the curve (AUC) was used to evaluate the model’s performance. Quantitatively, the results showed that the mean of the AUC values for lime (16SrII-B) and alfalfa (16SrII-D) future distribution for the periods of 2021–2040, 2041–2060, 2061–2080, and 2081–2100 were rated as “excellent”, with the values for the specified time periods being 0.859, 0.900, 0.931, and 0.913 for 16SrII-B; and 0.826, 0.837, 08.58, and 0.894 for 16SrII-D respectively. In addition, this study identified the hotspots and proportions of the areas that are vulnerable under the projected climate-change scenarios. The area of current (2021–2040) highly suitable distribution within the entire country for 16SrII-D was 19474.2 km2 (7.1%), while for 16SrII-B, an area of 8835 km2 (3.2%) was also highly suitable for the disease distribution. The proportions of these suitable areas are very significant from the available arable land standpoint. Therefore, the results from this study will be of immense benefit and will also bring significant contributions in mapping the areas of witches’ broom diseases in Oman. The results will equally aid the development of new strategies and the formulation of agricultural policies and practices in controlling the spread of the disease across Oman.
Highlights
Citrus fruits are considered to be a major crop across the world, with about 60 million megatons each year produced according to the Food and Agriculture Organization of the United Nations (FAO) (2015) data
The identifications and classifications of phytoplasmas of acid lime trees and alfalfa infected with phytoplasma disease were proven
This indicated that the bioclimatic variables set for 16SrII-D and 16SrII-B
Summary
Citrus fruits are considered to be a major crop across the world, with about 60 million megatons each year produced according to the Food and Agriculture Organization of the United Nations (FAO) (2015) data. Witches’ broom diseases (WBDs) have negatively impacted several high-value agricultural products in Oman, such as acid lime (Citrus aurantifolia L.) trees and the alfalfa (Medicago sativa L) crop. These diseases are caused by phytoplasmas related to the 16SrII-B and 16SrII-D subgroups [1,2]. The 16SrII-D phytoplasma is more aggressive than the 16SrII-B type. Plants infected with 16SrII-D phytoplasma show many symptoms including phyllody and witches’ broom. In Oman, 16SrII-D phytoplasma was reported in more than 25 plant hosts from economic crops and wild plants [3]
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