Generating virus-free cassava plants by in vitro propagation with chemical and heat treatment

Abstract

Cassava production in eastern and Central Africa is severely threatened by the current epidemic of cassava brown streak disease (CBSD). The disease is caused by cassava brown streak virus (CBSV)and Ugandan cassava brown streak virus (UCBSV) of the genus Ipomovirus, family Potyviridae. Using virus-free planting material is one effective way to reduce CBSD yield losses in farmer fields. The effects of chemical and heat treatment on tissue cultured plants was investigated to eliminate CBSV and UCBSV infections in three cassava varieties with differing levels of resistance to CBSD. Cassava node buds taken from young shoots of the varieties Kaleso (CBSD resistant), Kiroba (tolerant) and Albert (susceptible) infected with CBSV and UCBSV were grown in vitro in standard Murashige and Skoog tissue culture media, which alone eliminated viruses from up to 30% of the plants. To increase the number of virus-free plants, two-week old virus-infected in vitro plants were exposed to constant temperature regimes of 30, 35, 40 or 45°C for three weeks. Heat treatment at 40°C had the optimum effect as up to 50% virus-free plants were obtained for Kiroba; however, incubation at 45°C was lethal to all three varieties while the lower temperatures produced fewer virus-free plants. Chemical treatment of in vitro plants was performed using the antiviral chemical ribavirin at various concentrations. Ribavirin at 0.10 mM generated up to 40% virus-free plants in all three varieties but concentrations of 0.21 mM were lethal. These findings indicate important methods to produce virus-free planting material; their use by breeders and in the field, will help develop effective control strategies for CBSD management.

A novel seed treatment-based multiplication approach for cassava planting material

“…Numerous procedures already exist for rapid production of vegetatively propagated planting material. These include in-vitro techniques for clonal multiplication [29], micropropagation of meristem cultures [30,31], as well as approaches based on two-node seed pieces which are planted under controlled conditions and require transplanting upon seedling establishment [32]. Thus, these methods tend to be costly both in terms of equipment and infrastructure, potentially preventing their large-scale use to provide farmers with planting material PLOS ONE [33].…”

A method for generating virus-free cassava plants to combat viral disease epidemics in Africa

“…Surveillance of each plant throughout the three-month growth period was critical because some tolerant varieties have longer incubation periods before the expression of viral symptoms. A three-month growth period thus minimises false positives (plants incorrectly identified as virus-free) and reduces the number of plants that need to be confirmed virus-free by PCR and subsequent tissue culturing in Phase II [23]. A critical examination of symptoms therefore saves both time and resources while minimising the multiplication of virus-infected plants.…”

“…Such protocols are also adapted by the regulatory bodies in Ethiopia and Tanzania for generating certified seeds of sweetpotatoes [22]. In Africa and elsewhere, virus-free planting materials have been developed for several other crops including banana, citrus and cassava for providing healthy planting material to farmers for increased yields [20,23,24]. In this paper, we describe the use of such virus-indexing protocols at a regional level for cleaning cassava from five eastern and southern African countries of Kenya, Tanzania, Uganda, Malawi and Mozambique in the project “Cassava varieties and Clean seed to Combat CBSD and CMD project (5CP)” for providing virus-free planting material to the affected farmers.

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Incidence and Distribution of Rice Yellow Mottle Virus Disease in Kebbi State, Nigeria

“…RYMVD severity were expressed using an arbitrary scale indicating the extent of symptom development [12,8,5,7,13] [14,15,16] as follows: 1 = no visible RYMVD symptoms, 2 = mild foliar symptoms on some leaves, 3 = pronounced foliar symptoms but no die-back, 4 = pronounced foliar symptoms which might include slight die-back of terminal branches, and 5 = severe foliar symptoms and plant die-back [14,15,16].For each plant show symptoms of RYMVD were counted and recorded.…”