Stacking disease resistance and mineral biofortification in cassava varieties to enhance yields and consumer health

Abstract

Summary Delivering the benefits of agricultural biotechnology to smallholder farmers requires that resources be directed towards staple food crops. To achieve effect at scale, beneficial traits must be integrated into multiple, elite farmer‐preferred varieties with relevance across geographical regions. The staple root crop cassava (Manihot esculenta) is consumed for dietary calories by more than 800 million people, but its tuberous roots provide insufficient iron and zinc to meet nutritional needs. In Africa, cassava yields are furthermore limited by the virus diseases, cassava mosaic disease (CMD) and cassava brown streak disease (CBSD). In this study, we strove to develop cassava displaying high‐level resistance to CBSD and CMD to attain food and economic security for cassava farmers, along with biofortified levels of iron and zinc to enhance consumer health. RNAi‐mediated technology was used to achieve resistance to CBSD in two East African and one Nigerian farmer‐preferred cultivars that harboured resistance to CMD. The Nigerian cvs. TMS 95/0505 and TMS 91/02324 were modified with T‐DNA imparting resistance to CBSD, along with AtIRT1 (major iron transporter) and AtFER1 (ferritin) transgenes to achieve nutritionally significant levels of iron and zinc in cassava storage roots (145 and 40 µg/g dry weight, respectively). The inherent resistance to CMD was maintained in all four disease resistant and mineral enhanced cassava cultivars described here, demonstrating that this technique could be deployed across multiple farmer‐preferred varieties to benefit the food and nutritional security of consumers in Africa.

Genome‐wide association studies reveal genetic basis of ionomic variation in cassava

“…The cassava storage root is rich in starch and contains 116 kilocalories per 100 grams of edible cassava storage root. Therefore, cassava storage root is the main source of dietary calories for people in sub-Saharan Africa Hu, Ji, Shi, et al 2021;Narayanan et al, 2021). Currently, up to 2 billion people suffer from iron and zinc deficiency globally (Huang et al, 2020).…”

Mutations in DNA polymerase δ subunit 1 mediate CMD2-type resistance to Cassava Mosaic Geminiviruses

“…The full-length cDNA of MePOLD1 was amplified from cassava plant line 5001-NASE 14-#41 43 . Primers were designed to be specific for the haplotype carrying the resistance MePOLD1 allele and PCR performed.…”

“…NASE14 (the line formerly known as MM96/4271) was developed by crossing in a breeding program at the International Institute for Tropical Agriculture 42 and does not lose resistance after passage through culture-induced morphogenesis 12 . However, we previously reported an exception: in experiments where NASE14 was used to generate transgenic lines all but one of the transgenic events remained resistant to CMD 43 . To understand this unexpected outcome, targeted Sanger sequencing of MePolD1 was performed on the transgenic line 5001-NASE14-#41 that had lost CMD2 resistance.…”

Studies on Pure Mlb® (Multiple Left Border) Technology and Its Impact on Vector Backbone Integration in Transgenic Cassava

“…Also, the correlation studies between copy number and VBB indicate that increasing the frequency of VBB free transgenic events results in a proportionate increase in the low-copy events. Based on this study, Mlb R technology (Triple LB) was incorporated in the routine transgenic cassava pipeline (Beyene et al, 2017;Narayanan et al, 2019Narayanan et al, , 2021.…”