Genetic gains with genomic versus phenotypic selection for drought and waterlogging tolerance in tropical maize(Zea mays L.)

Erratic rainfall often results in intermittent drought and/or waterlogging and limits maize(Zea mays L.)productivity in many parts of the Asian tropics.Developing climate-resilient maize germplasm possessing tolerance to these key abiotic stresses without a yield penalty under optimal growing conditions is a challenge for breeders working in stress-vulnerable agro-ecologies in the region.Breeding stress-resilient maize for rainfed stress-prone ecologies is identified as one of the priority areas for CIMMYT-Asia maize program.We applied rapid cycle genomic selection(RCGS)on two multiparent yellow synthetic populations(MYS-1 and MYS-2)to improve grain yield simultaneously under drought and waterlogging conditions using genomic-estimated breeding values(GEBVs).Also,the populations were simultaneously advanced using recurrent phenotypic selection(PS)by exposing them to managed drought and waterlogging and intermating tolerant plants from the two selection environments.Selection cycles per se(C1,C2,and C3)of the two populations developed using RCGS and PS approach and their test-cross progenies were evaluated separately in multilocation trials under managed drought,waterlogging,and optimal moisture conditions.Significant genetic gains were observed with both GS and PS,except with PS in MYS-2 under drought and with GS in MYS-1 under waterlogging.Realized genetic gains from GS were relatively higher under drought conditions(110 and 135 kg ha^(-1) year^(-1))compared to waterlogging(38 and 113 kg ha^(-1) year^(-1))in both MYS-1 and MYS-2,respectively.However,under waterlogging stress PS showed at par or better than GS as gain per year with PS was 80 and 90 kg ha^(-1),whereas with GS it was 90 and 43 kg ha^(-1) for MYS-1 and MYS-2,respectively.Our findings suggested that careful constitution of a multiparent population by involving trait donors for targeted stresses,along with elite highyielding parents from diverse genetic background,and its improvement using RCGS is an effective breeding approach to build multiple stress tolerance without compromising yield when tested under optimal conditions.

Fitness-related selection on floral traits in the distylous plant Primula poissonii (Primulaceae)

Aims Reproductive fitness of different floral phenotypes varies within and/or among populations.These variations are important to understand the process of natural selection and the evolution of floral traits.In this study,we focused on a distylous,self-incompat-ible species,Primula poissonii,to investigate fitness-related selec-tion on floral traits.Our aim was to determine how traits vary as targets of natural selection and whether morph-specific selection occurs.Methods This study was conducted at two sites(Yushuizhai at 2700 m and Haligu at 3200 m)in the Lijiang Alpine Botanical Garden,northwest-ern Yunnan,southwestern China.Insects visiting flowers of P.pois-sonii were observed,captured and identified.Randomly selected plants of long-and short-styled morphs were labeled.Five floral/inflorescence traits were measured including floral display,corolla width(CW),floral tube length(FTL),tube opening width(TOW)and floral scape height.Fruit and seed set were recorded.The total num-ber of seeds per individual plant(plant fitness)and seed production per capsule(flower fitness)were calculated.Multiple regression analyses were used to quantify selection gradients.Important Findings The frequencies of the two morphs did not deviate from the expected 1:1 ratio at both sites.Except for FTL,the four other traits did not dif-fer significantly between the long-and short-styled morphs.Floral scape height,floral display and FTL differed between two sites.The selection regimes differed between two morphs and between two sites.At the Yushuizhai site,linear selection for shorter floral tubes was stronger in the short-styled morph.However,nonlinear selec-tion on the floral display was stronger in the long-styled morph than selection on the short-styled morph.At the Haligu site,linear selec-tion for a smaller corolla was stronger in the long-styled morph.A morph-specific nonlinear selection on CW and floral display was also detected.Morph-specific selections were detected through the estimation of flower fitness only in Haligu population.In this site,morph-specific linear selection was also detected for CW and floral display.Morph-specific nonlinear selection on traits was detected only in CW.We found that butterflies and sphingid moths dominated at Yushuizhai,while long-tongued bees dominated at Haligu.The difference in pollinator fauna suggested that selection on floral tubes may be due to differences in pollinator assemblages.Overall,variation of floral and/or inflorescence traits in P.poissonii was probably driven by pollinator selection.Selection regime dif-ferences between two morphs,in part,due the inter-morph diver-gences of sexual functions in distylous plant.

A Pyramid Breeding of Eight Grain-yield Related Quantitative Trait Loci Based on Marker-assistant and Phenotype Selection in Rice(Oryza sativa L.)

1000-Grain weight and spikelet number per panicle are two important components for rice grain yield. In our previous study, eight quantitative trait loci （QTLs） conferring spikelet number per panicle and 1000-grain weight were mapped through sequencing-based genotyping of 150 rice recombinant inbred lines （RILs）. In this study, we validated the effects of four QTLs from Nipponbare using chromosome segment substitution lines （CSSLs）, and pyramided eight grain yield related QTLs. The new lines containing the eight QTLs with positive effects showed increased panicle and spikelet size as compared with the parent variety 93-11. We further proposed a novel pyramid breeding scheme based on marker-assistant and phenotype selection （MAPS）. This scheme allowed pyramiding of as many as 24 QTLs at a single hybridization without massive cross work. This study provided insights into the molecular basis of rice grain yield for direct wealth for high-yielding rice breeding.