Identifying New Resistance to Cassava Mosaic Disease and Validating Markers for the CMD2 Locus

Cu Thi Le Thuy,Nguyen Huu Hy,Nguyen Thi Hanh,Xiaofei Zhang,Pham Thi Thu Ha,Ismail Rabbi ,Do Thi Nhu Quynh,Xuan Hoi Pham,Phạm Thị Thanh Nhàn ,Nguyẽn Mạnh Hùng ,Nguyen Ba Tung,Nguyen Trong Hien,Jonathan C Newby ,Luis Augusto Becerra Lopez‐Lavalle ,Peter Kulakow ,Nguyen Anh Vu,Le Ngoc Tuan,Đỗ Thị Trang ,Lê Huy Hàm ,Hernán Ceballos

doi:10.3390/agriculture11090829

Abstract

Cassava (Manihot esculenta Crantz) is a crucial staple crop, and provides carbohydrate energy to more than half a billion people in the tropics. Cassava mosaic disease (CMD) is the most important disease of cassava in Africa. Since Sri Lanka Cassava Mosaic Virus (SLCMV) was first reported in South East Asia in 2015, establishing sustainable solutions to CMD has become a top priority for the cassava program at the International Center for Tropical Agriculture (CIAT) and its partners. In the present study, we screened two populations for CMD resistance: VNM142, 142 clones collected from farms throughout Vietnam, and CIAT102, 102 clones resistant to CMD or mites, which were introduced from CIAT. High broad-sense heritability was observed in all the trials (>0.80). From the population VNM142, eight clones showed high CMD resistance with CMD severity scores less than 2.0. Two resistant clones had the same DNA fingerprinting with the accessions CR63 (PER262 or TAI9) and KM57 (VNM8) in the genebank, respectively. To our knowledge, this is the first report of CMD resistance in the genebank at CIAT. We also used the two populations to validate the CMD markers S12_7926132 and S14_4626854. Both markers explained 51% of the population variance in the segregating population CIAT102, but only 11% in the diverse population VNM142. Thus, we concluded that the two CMD markers could not be used to select for CMD resistance in diverse populations, but could predict the CMD resistance in segregating populations when the susceptible parents do not have resistant marker alleles and the resistance of the CMD2 donors is confirmed.

Highlights

Cassava (Manihot esculenta Crantz) provides the third-largest source of food carbohydrates in the tropics, after rice and maize
The introduced population, CIAT102, was derived from CMD2 donors, C-clones, which were the progeny of the cassava mosaic disease (CMD)-resistant clones in Africa, TME3 [16]
The CMD2 resistance was confirmed in the CIAT102 clones because 34 clones were asymptomatic when exposed to the Sri Lanka Cassava Mosaic Virus (SLCMV)

Summary

Introduction

Cassava (Manihot esculenta Crantz) provides the third-largest source of food carbohydrates in the tropics, after rice and maize. Cassava is usually grown by smallholder farmers and feeds more than half a billion people worldwide [1]. It is a major staple crop in developing countries, especially in sub-Saharan Africa. In South East Asia (SEA), cassava has become an importance crop for rural livelihoods and economic development [4]. It was estimated that more than 8 million farmers grow cassava in SEA, covering approximately 3.9 million ha and accounting for 25% of the global production [2]. Due to the strong market demand, cassava production has increased in the region with rapid expansion to Cambodia, Lao PDR, and Myanmar. Cassava mosaic disease (CMD) is spreading in the region, which caused a yield loss between 30% and 50% from the secondary infection [5]

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Methods

Conclusion