Quantitative trait loci for soil-penetrating ability of roots in durum wheat

Increasing root penetration (RP) ability into hard soil is important to improve drought resistance in durum wheat. Traits related to RP ability were evaluated in 110 recombinant inbred lines (RILs) derived from a cross between 'Jennah Khetifa' and 'Cham1' using paraffin-Vaseline (PV) discs. QTL analyses were made for the number of roots penetrating the PV disc (PVRN), total number of seminal and crown roots (TRN), RP index (PVRN/TRN) and root dry weight (DW). 'Jennah Khetifa' had higher PVRN, RP index and root DW values than 'Cham1', and the RILs showed significant differences for these traits. Two closely-linked markers, Xgwm617a and Xgwm427b , on the long arm of chromosome 6A were associated with PVRN and RP index. For root DW, a QTL was linked to marker Xgwm11 on chromosome 1B. Alleles of 'Jennah Khetifa' were associated with increased PVRN, RP index and root DW. No QTL was detected for TRN in this mapping population. The absence of co-located QTLs suggested that RP ability was controlled separately from TRN and root DW. Although the population size and number of replications were small, this study helps in understanding the complexity of root growth and the potential of marker-assisted selection for selecting genotypes with high RP ability in durum wheat populations.     

Variation in root penetration ability, osmotic adjustment and dehydration tolerance among accessions of rice adapted to rainfed lowland and upland ecosystems

Drought is the major constraint limiting rainfed rice production. The ability of rice roots to penetrate compacted soils and therefore to increase water extraction capacity, osmotic adjustment and dehydration tolerance of leaves enables the plant to tolerate drought. Experiments were conducted to determine the extent of genetic variation in root penetration index, osmotic adjustment and dehydration tolerance among indica accessions adapted to rainfed lowlands as well as traditional varieties from rainfed uplands. Root penetration index was evaluated in a system using wax–petrolatum layers to simulate soil compaction. Osmotic adjustment and dehydration tolerance were studied under slow development of water stress. Substantial genetic variation was found for root penetration index, osmotic adjustment and dehydration tolerance among indica ecotypes from lowlands, and the study of several traditional varieties from uplands showed variation in root penetration index and related root traits. An indica accession, IR58821‐23‐B‐1‐2‐1 had a high root penetration index of 0.38. The accessions, IR61079‐33‐1‐2‐2‐3, IR62266‐42‐6‐2 and IR63919‐38‐B‐1 had high osmotic adjustment capacities (1.91, 1.90 and 1.78 MPa, respectively); IR61079‐33‐1‐2‐2‐3 also had high dehydration tolerance. Good osmotic adjustment and dehydration tolerance were associated with poor root system. The traditional varieties ‘Kallurundaikar’ and ‘Norungan’ had higher root penetration indices (0.46 and 0.43, respectively), than even the japonica accessions. The study identified indica accessions and traditional varieties with superior root‐ and shoot‐related drought resistance traits that could be used in breeding for drought resistance in rice.     

Chromosomal location of genes for resistance to powdery mildew in common wheat (Triticum aestivum L. em Thell.). 9. Gene MlZec1 from the Triticum dicoccoides-derived wheat line Zecoi-1

The Triticum dicoccoides-derived wheat line Zecoi-1 provides effective protection against powdery mildew. F₃ segregation analysis of Chinese Spring × Zecoi-1 hybrids showed that resistance in line Zecoi-1 is controlled by a single dominant gene. Amplified fragment length polymorphism (AFLP) analysis of bulked segregants from F₃s showing the homozygous resistant and susceptible phenotypes identified eight markers, of which four were associated with the resistance allele in repulsion phase. Following the assignment of these four repulsion phase AFLP markers to wheat chromosome 2B with the aid of Chinese Spring nulli-tetrasomic lines, they were physically mapped in the terminal breakpoint interval 0.89 (2BL-6)–1.00 (telomere) of chromosome 2BL. Genetic and physical mapping of simple sequence repeat markers from the distal half of chromosome 2BL located the wild emmer-derived powdery mildew resistance gene distal of breakpoint 0.89 in deletion line 2BL-6. Based on disease response patterns, genomic origin and chromosomal location the resistance gene in Zecoi-1 is temporarily designated MlZec1.