Ana Clara Pontaroli

Spike fertility index (also known as fruiting efficiency) at maturity (FE_m: grain number per spike g^–1 spike chaff at maturity) and spike harvest index (SHI: grain weight per spike g^–1 spike chaff weight at maturity) are considered promising selection criteria for improving grain yield (GY) in bread wheat (Triticum aestivum L.). However, their usefulness in early generations remains to be established. Here, a population derived from a cross between ‘Baguette 10’ and ‘Klein Chajá’ was evaluated from early generations (F₂–F₃) to recombinant inbred lines (RIL). Associations of FE_m and SHI measurements between early generations and RIL were established. Also, responses in grain number m^–2 (GN) and GY in the RIL after simulated selection for high FE_m or high SHI in the F₂–F₃ were assessed. Positive correlations were found in FE_m measured in the F₂–F₃ vs. in the RIL (r = .32, P < .05) and SHI measured in the F₃ vs. in the RIL (r = .26, P < .05). After selection for high FE_m in the F₂–F₃, responses in GN were always positive: GN increased by 5.1–22.1% depending on the selection strategy. Responses in GY were positive in three out of four selection strategies, averaging –1.3–2.1%. Responses to selection in GN and GY in the RIL using SHI as a selection criterion in the F₂–F₃ were negative or neutral. Our results support the use of FE_m as a selection criterion in early generations for increasing GN and GY in advanced generations of bread wheat‐breeding programs.

Fusarium head blight (FHB) remains a devastating disease in bread wheat (Triticum aestivum L.) and other small grains. Genetic resistance to FHB is a complex trait; in addition to active physiological resistance, plant developmental and morphological traits may indirectly affect disease progression and provide a passive mechanism of resistance. In this study, we investigated the relationship between FHB type II resistance and spike architecture traits in a recombinant inbred line (RIL) population of bread wheat. Disease resistance traits were FHB severity at 21 days post inoculation (dpi) and area under the disease progress curve (AUDPC). Spike architecture traits measured were rachis length, spike density, number of spikelets per spike, florets per spike and florets per spikelet. The RIL population showed significant variation for all traits. Heritability values were moderate to high for FHB severity (0.69) and AUDPC (0.63) and high for the spike architecture traits (0.74 - 0.92). FHB severity and AUDPC showed a moderate and significant association with the number of florets per spike (r = 0.38 and r = 0.31, respectively) and with the number of florets per spikelet (r = 0.28 and r = 0.27, respectively), reflecting a greater spread of the fungus in spikes with higher floret number. These results suggest that the number of florets per spike and the number of florets per spikelet should be considered in FHB resistance breeding efforts, because selection of lines with higher number of florets could lead to a correlated selection response towards increased FHB levels under field conditions.

Fruiting efficiency (FE, grains per g of spike dry weight at anthesis) was proposed as a promising spike trait to improve wheat yield potential, based on its functional relationship with grain number determination and the evidence of trait variability in elite germplasm. During the last few years, we have witnessed great advances in the understanding of the physiological and genetic basis of this trait. The present review summarizes the recent heritability estimations and the genetic gains obtained when fruiting efficiency was measured at maturity (FEm, grains per g of chaff) and used as selection criterion. In addition, we propose spike ideotypes for contrasting fruiting efficiencies based on the fertile floret efficiency (FFE, fertile florets per g of spike dry weight at anthesis) and grain set (grains per fertile floret), together with other spike fertility-related traits. We also review novel genes and quantitative trait loci available for using marker-assisted selection for fruiting efficiency and other spike fertility traits. The possible trade-off between FE and grain weight and the genes reported to alter this relation are also considered. Finally, we discuss the benefits and future steps towards the use of fruiting efficiency as a selection criterion in breeding programs.

Spike fertility index (SF) is a trait easily measured at maturity and strongly associated with the number of grains per unit area. In order to identify genomic regions involved in SF control, a biparental (Baguette 10 × Klein Chajá) population of 80 recombinant inbred lines (RIL) was used. Seven field trails were conducted to determine the SF BLUP value per RIL. RILs were genotyped using a commercial chip (Axiom® 35K SNP Wheat Breeder's Array, Affimetrix). A linkage map was constructed with 857 SNP markers, and SF QTL mapping was performed. The narrow-sense heritability of SF was 0.89. Three genomic regions (QTL) associated with SF were found on chromosomes 2D, 4A, and 7A. The proportion of genetic variation explained by these three QTL was 32%, with no significant epistatic interaction between QTL.

Spike fertility index (SF) has been proposed as a promising selection criterion for increasing grain yield (GY) in bread wheat. Here, changes in GY and related traits after simulated selection (10% intensity) for high SF or high GY per se were assessed in two RIL populations: (I) Avalon/Glupro and (II) Baguette 10/Klein Chajá, and in (III) advanced lines from a breeding program. Grain yield, SF, grain number per unit area (GN), grain weight (GW), test weight (TW) and grain protein content (GPC) were determined. Regardless of the environmental conditions, simulated selection for high SF always resulted in GN increases (between 1.6 and 27.4%). Average GY increase observed after selection for high SF (11.5%; N=10; SEM=5.8) did not differ (p=0.92) from the average GY increase observed after selection for GY per se (11.8%; N=10; SEM=4.9). Grain weight, GPC and TW tended to decrease with selection for high SF; however, these trade-offs might be avoided by concurrent selection. Our findings validate the use of SF as a selection criterion for increasing grain yield in bread wheat.

Biotrophic disease is one of the largest causes of decreased yield in agriculture. While exposure to ultraviolet B (UV-B) light (280–320 nm) has been previously observed to reduce plant susceptibility to disease, there is still a paucity of information regarding underlying biological mechanisms. In addition, recent advances in UV-LED technology raise the prospect of UV light treatments in agriculture which are practical and efficient. Here, we characterized the capability of UV-B LED pre-treatments to reduce susceptibility of a range of lettuce (Lactuca sativa) cultivars to downy mildew disease caused by the obligate biotroph Bremia lactucae. Innate cultivar susceptibility level did not seem to influence the benefit of a UV-B induced disease reduction with similar reductions as a percentage of the control observed (54–62% decrease in conidia count) across all susceptible cultivars. UV-B-induced reductions to conidia counts were sufficient to significantly reduce the infectivity of the diseased plant. Secondary infections caused by UV-B pre-treated plants exhibited yet further (67%) reduced disease severity. UV-B-induced flavonoids may in part mediate this reduced disease severity phenotype, as B. lactucae conidia counts of lettuce plants negatively correlated with flavonoid levels in a UV-B-dependent manner (r = −0.81). Liquid chromatography–mass spectrometry (LC-MS) was used to identify metabolic features which contribute to this correlation and, of these, quercetin 3-O-(6”-O-malonyl)-b-D-glucoside had the strongest negative correlation with B. lactucae conidia count (r = −0.68). When quercetin 3-O-(6”-O-malonyl)-b-D-glucoside was directly infiltrated into lettuce leaves, with those leaves subsequently infected, the B. lactucae conidia count was reduced (25–39%) in two susceptible lettuce cultivars. We conclude that UV-B induced phenolics, in particular quercetin flavonoids, may act as phytoanticipins to limit the establishment of biotrophic pathogens thus delaying or reducing their sporulation as measured by conidia count. These findings highlight the opportunity for UV-B morphogenesis to be exploited through the application of UV-LED technology, as part of the development of next-generation, sustainable disease control tools.

Background: Increasing wheat (Triticum aestivum L.) production is required to feed a growing human population. In order to accomplish this task a deeper understanding of the genetic structure of cultivated wheats and the detection of genomic regions significantly associated with the regulation of important agronomic traits are necessary steps. To better understand the genetic basis and relationships of adaptation and yield related traits, we used a collection of 102 Argentinean hexaploid wheat cultivars genotyped with the 35k SNPs array, grown from two to six years in three different locations. Based on SNPs data and gene-related molecular markers, we performed a haplotype block characterization of the germplasm and a genome-wide association study (GWAS). Results: The genetic structure of the collection revealed four subpopulations, reflecting the origin of the germplasm used by the main breeding programs in Argentina. The haplotype block characterization showed 1268 blocks of different sizes spread along the genome, including highly conserved regions like the 1BS chromosome arm where the 1BL/1RS wheat/rye translocation is located. Based on GWAS we identified ninety-seven chromosome regions associated with heading date, plant height, thousand grain weight, grain number per spike and fruiting efficiency at harvest (FEh). In particular FEh stands out as a promising trait to raise yield potential in Argentinean wheats; we detected fifteen haplotypes/markers associated with increased FEh values, eleven of which showed significant effects in all three evaluated locations. In the case of adaptation, the Ppd-D1 gene is consolidated as the main determinant of the life cycle of Argentinean wheat cultivars. Conclusion: This work reveals the genetic structure of the Argentinean hexaploid wheat germplasm using a wide set of molecular markers anchored to the Ref Seq v1.0. Additionally GWAS detects chromosomal regions (haplotypes) associated with important yield and adaptation components that will allow improvement of these traits through marker-assisted selection.