Detection, virulence and genetic diversity of Fusarium species infecting tomato in Northern Pakistan.

Asma Akbar,Kaleem Ullah,Muhammad Fahim,Gul Shad Ali,Shaukat Hussain,Ulrich Melcher

doi:10.1371/journal.pone.0203613

Abstract

In addition to the well-known Fusarium oxysporum f.sp. lycopersici, several other Fusarium species are known to cause extensive worldwide crop losses in tomatoes. Prevalence and identities of Fusarium species infecting tomatoes in Northwest Pakistan is currently not known. In this study, we surveyed and characterized Fusarium species associated with symptomatic tomatoes in Northwest Pakistan using morphological and molecular analyses. Pathogenicity tests revealed varying degrees of virulence with some Fusarium sp. causing severe disease symptoms whereas others displaying mild symptoms. Molecular identification based on Internal Transcribed Spacer (ITS) region and TEF-1α gene sequencing classified all isolates into four major species with a majority (68.9%) belonging to Fusarium incarnatum-equiseti species complex (FIESC), followed by F. graminearum (20.7%), F. acuminatum (6.8%), and F. solani (6.8%). ISSR analyses revealed substantial genetic variability among all the Fusarium population infecting tomatoes. Genetic distance between populations from the central region and the type strain F.o. f.sp. lycopersici from Florida was the highest (0.3662), whereas between the south and central region was the lowest (0.0298), which showed that genetic exchange is negatively effected by distance. High genetic variability suggests that these Fusarium species have the potential to become a major production constraint for tomato growers. Findings in this report would greatly facilitate identification of Fusarium species in developing countries and would provide groundwork for devising and implementing disease management measures for minimizing losses caused by Fusarium species in tomatoes.

Highlights

Tomato (Solanum lycopersicum), a member of family Solanaceae, is considered one of the world’s most important and popular vegetables [1]
Multiple comparison tests of the lesion size data showed no significant difference among most isolates except Pak-1 and Pak-6, which were classified as highly virulent with lesion sizes of 6 and 7 mm, respectively (Fig 2)
Our study shows that Fusarium wilt is present in a majority of the tomato growing areas at all growth stages, most likely because of lack of sanitation, using infected seeds, and mono-culturing, which could lead to build-up of soil-borne inoculum

Summary

Introduction

Tomato (Solanum lycopersicum), a member of family Solanaceae, is considered one of the world’s most important and popular vegetables [1]. Consumption and demand for tomatoes are increasing steadily due to increase in population, and it is available at a lower price in comparison to other vegetables with higher nutritional values. It is consumed as ketchup, sauces, a fresh vegetable, and more in many home-cooked and restaurant-served meals. Pakistan exported 9832 tons of tomatoes from 2009–2010 valued at 77 million rupees During this time period, the production area increased from 27.9 to 50 thousand hectares, with an increase in yield from 268.8 to 476.8 thousand tons. Europe and America are the major sources of commercially grown cultivars that are introduced to the country [3]

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Results

Conclusion