Response to early drought stress and identification of QTLs controlling biomass production under drought in pearl millet

Abstract

34Pearl millet plays a major role in food security in arid and semi-arid areas of Africa and 35 India. However, it lags behind the other cereal crops in terms of genetic improvement. The 36 recent sequencing of its genome opens the way to the use of modern genomic tools for 37 breeding. Our study aimed at identifying genetic components involved in early drought stress 38 tolerance as a first step toward the development of improved pearl millet varieties or 39 hybrids. A panel of 188 inbred lines from West Africa was phenotyped under early drought 40 stress and well-irrigated conditions. We found a strong impact of drought stress on yield 41 components. This impact was variable between inbred lines. We then performed an 42 association analysis with a total of 392,493 SNPs identified using Genotyping-by-Sequencing 43 (GBS). Correcting for genetic relatedness, genome wide association study identified QTLs for 44 biomass production in early drought stress conditions and for stay-green trait. In particular, 45 genes involved in the sirohaem and wax biosynthesis pathways were found to co-locate with 46 association loci. Our results open the way to use genomic selection to breed pearl millet lines 47 100 row. Fertilization (NPK) followed standard recommendation i.e. 150 kg ha -1 of NPK (15-15-101 15) after sowing. Urea was applied at 100 kg ha -1 at two stages, 50 kg ha -1 after thinning and 102 50 kg ha -1 30 days after sowing. 103 The flowering date corresponding to 50% of plants flowering (in days after sowing) was 104 recorded. Height of the plant (in cm), panicle and stalk length (in cm), total number of leaves, 105 aerial biomass (Kg.plant -1 ), as well as stay-green trait (number of green leaves/total number of 106 leaves) were measured on 6 plants per plot at maturity. Shoots and panicles were harvested Bidinger FR, Mahalakshmi V, Rao GDP. Assessment of drought resistance in pearl 438 millet [ Pennisetum americanum (L.) Leeke]. 1. Factors affecting yield under stress. 439 Aust J Agric Res. 1987;38: 37-48. 440 441 6. Yadav RS, Hash CT, Bidinger FR, Cavan GP, Howarth CJ. Quantitative trait loci 442 associated with traits determining grain and stover yield in pearl millet under terminal 443 drought-stress conditions.

Development of a model estimating root length density from root impacts on a soil profile in pearl millet (Pennisetum glaucum(L.) R. Br). Application to measure root system response to water stress in field conditions

“…Soil water content was followed using Diviner probes and used to compute the fraction of transpirable soil water (FTSW) as previously described [14]. FSTW values below 40% indicate here water-limiting conditions [24].…”

“…Previous studies suggested that pearl millet tolerance to dry environments could be due to mechanisms regulating water use efficiency and limiting water loss rather than to improved water acquisition [29]. Interestingly, an expansion of gene families involved in cutin, suberin and wax biosynthesis was observed in pearl millet compared to other cereals and a potential QTL for biomass production under drought was found to co-locate with a gene encoding 3-ketoacyl-CoA synthase that catalyzes the elongation of C24 fatty acids during both wax and suberin biosynthesis [14] thus supporting the link between transpiration barriers and drought resistance in pearl millet. Experiments using lysimeters indicated that temporal patterns of water use, rather than total water uptake, were essential for explaining the terminal drought tolerance of pearl millet genotypes containing a terminal drought tolerance QTL [30].…”

“…Soil in the field trials was sandy and had the typical characteristics of the West Africa Sahelian soils in which pearl millet is grown. Tillage and chemical fertilization were applied as recommended for pearl millet [14]. Weeding was performed before planting.…”

“…At 72 DAP irrigation was resumed until the end of the growth cycle in addition with the first rain in June (S2 Fig). Field dry-down was monitored by measuring volumetric soil moisture to evaluate the fraction of transpirable soil water (FTSW) using Diviner probes (Sentek Pty Ltd) as previously described [14].…”

Plausible association between drought stress tolerance of barley (Hordeum vulgare L.) and programmed cell death via MC1 and TSN1 genes

“…One main concern is that the importance of each gene involved in the stress response is not the same, meaning that different genes have different impact on stress tolerance as some genes are more important than others. This concept has been well studied in drought stress quantitative trait loci experiments (Fan et al , Honsdorf et al , Ahmad et al , Debieu et al ). However, at the molecular level, this concept is not well understood.…”