Durum wheat breeding manual 2020-2025

Abstract

A product profile breeding strategy aims to: i) identify the main competitors (existing cultivars), their advantages and limitations, and the use of these to define the additional traits needed to replace them in the market; ii) reduce breeding time, costs, and efforts to deliver the best possible new cultivar; and iii) determine the true breeding targets (clients and agro-ecologies) and use them to Drive the selection strategy.

The durum wheat breeding program of the International Center for Agricultural Research in the Dry Areas (ICARDA) aims to deliver new varieties that respond to the Sustainable Development Goals (SDGs) of SDG1: no poverty; and SDG2: zero hunger across several developing countries, with a focus on non-tropical Drylands. Within these goals, the specific product profiles (PPs) are identified in interaction with the National Agricultural Research System (NARS) partners. Each PP corresponds to a targeted population of environments (TPE), which is identified by means of a principal component analysis (GGE) of Stage 4 yield trials combined with climatic and social characterizations. Each PP is also assigned a weighted selection index to effectively select for the most critical traits. In the Stage 2, 3 and 4 yield trials, each entry is defined as matching a given PP when it shows high yield in the station that better represent the TPE of that PP, and a high score for the related selection index. An elite is deemed ready to advance to Stage 5 when addition of the two scores also matches the required phenology and height characteristics.

The overall breeding strategy is to design targeted crosses and advance generations rapidly to F1:4 by means of selected bulks and shuttle breeding to avoid imposing stringent selections outside the TPE. The F4 are then assessed across TPE and advanced via pedigree to F5 in the off-season. Stage 1 yield testing is also conducted outside the TPE due to logistic considerations, and only traits that are common across PPs are selected. Stage 2 is conducted across TPE to evaluate stability (GxE), a critical trait for climatic adaptation, and performance in the specific TPE. Stage 3 are tested directly at the target environment of each PP by NARS partners. Stage 4 are selected via Stage 3 results, and equally tested by NARS partners.

The general strategy for population enrichment aims to hybridize Stage 2, 3, and 4 entries with good matching (weighted index) to one or more PP. In addition, 2/5 of the crosses are made between the best Stage 4 entries and foreign germplasm coming from other breeding programs, pre-breeding efforts, and landraces. Wide-crosses are integrated at the F2 level via selection of germplasm produced by the genebank between Stage 4 and wild relatives. A step of recurrent genomic sequencing (GS) is incorporated at the F4 level for the most promising crosses.

Two parallel breeding programs are conducted in Lebanon (Terbol) and Morocco (Marchouch) to target West-Asian and North African TPE, respectively. In addition, a facultative winter program is conducted in Lebanon (Kfardan) and Morocco (Annoceur) for specific PPs. A further three breeding programs for selection among F1:5 are run by NARS partners in Ethiopia (Debre Zeit), India (Amalaha) and Senegal (Fanaye).

In total, six durum wheat breeding programs exist within ICARDA to serve eight mega PPs.

This document provides the reasoning, practical, and logistic details on how to convert this strategy into practice.