Yield Loss Associated with Different Levels of Stem Rust Resistance in Bread Wheat

Abstract

Puccinia graminis f. sp. tritici race Ug99 (syn. TTKSK) has been identified as a major threat to wheat production based on its broad virulence. Despite its importance, the effect of Ug99 on different types of resistance in wheat has not been thoroughly researched. In field trials conducted with P. graminis f. sp. tritici race PTKST (Ug99 race group) over 2 years, AUDPC differentiated the moderately susceptible variety SC Stallion (515) and susceptible entries SC Nduna (995) and Line 37-07 (1634) from those with adult plant resistance (APR). AUDPC of APR varieties W1406 (256), W6979 (399), and Kingbird (209) was higher than the mean of 25 recorded for the all stage resistant (ASR) variety SC Sky. In fungicide-protected and unprotected plots, race PTKST resulted in a mean yield loss of 21.3%, with susceptible Line 37-03 recording a 47.9% decrease in grain yield. Yield reduction in APR varieties reached 19.5% in W1406, whereas the ASR control SC Sky showed a mean loss of 6.4%. Although APR reduced the effects of stem rust on yield and yield components under conditions of high disease pressure, it did not provide the same protection as effective ASR.

Accomplishments in wheat rust research in South Africa

“…Wheat cultivars carrying the pleiotropic race non-specific APR genes Sr2/Yr30, Lr34/Yr18/Sr57, Lr46/Yr29/Sr58 and Lr67/Yr46/Sr55 have maintained moderate levels of rust resistance under epidemic field trial conditions in South Africa and might not provide adequate protection when deployed singly under high disease pressure. Soko et al 52 recorded grain yield losses due to stem rust of between 10.1% and 19.5% for APR cultivars as opposed to a 6.4% loss in an ASR line. Previously, Pretorius et al 8 mentioned losses as high as 65% for susceptible wheat cultivars infected with stripe rust and a 56% yield gain was obtained when leaf rust was controlled by fungicide application on a susceptible cultivar.…”

Selection Evaluation of Introgressive Lines of Soft Winter Wheat With Signs of Resistance to Phytopathogens

“…One of the factors limiting the yield of high yields of soft winter wheat Triticum aestivum L. are diseases, the losses of which can reach 15-30% or more (Soko et al, 2018). Since the selection of plants for immunity to diseases is the most effective means of their protection, a large-scale search for new sources of resistance and the creation of source material, in particular by remote hybridization (Warburton et al, 2006).…”

Registration of hard white winter wheat germplasms KS14U6380R5, KS16U6380R10, and KS16U6380R11 with adult plant resistance to stem rust

“…In four field seasons of trials in Kenya with the Ug99 race, Kingbird's field rust response ranged from 5 MSS (moderately susceptible to susceptible) to 5 MR (moderately resistant), while the susceptible (S) check reaction was 90–100 S (Njau et al., 2010). In a 2‐yr field study with the Ug99 group race PTKST, mean yield loss of the susceptible check cultivar was 47.9%, while mean yield loss of Kingbird was 10.1% (Soko, Bender, Prins, & Pretorius, 2018). Kingbird's field performance in Ethiopia against races TTKSK, TKTTF, TRTTF, and JRCQC was very good, with stem rust severities ranging from trace to 15% (Borlaug Global Rust Initiative, 2019; Hundie et al., 2019).…”