QTL mapping of agronomic waterlogging tolerance using recombinant inbred lines derived from tropical maize (Zea mays L) germplasm.

Waterlogging is an important abiotic stress constraint that causes significant yield losses in maize grown throughout south and south-east Asia due to erratic rainfall patterns. The most economic option to offset the damage caused by waterlogging is to genetically incorporate tolerance in cultivars that are grown widely in the target agro-ecologies. We assessed the genetic variation in a population of recombinant inbred lines (RILs) derived from crossing a waterlogging tolerant line (CAWL-46-3-1) to an elite but sensitive line (CML311-2-1-3) and observed significant range of variation for grain yield (GY) under waterlogging stress along with a number of other secondary traits such as brace roots (BR), chlorophyll content (SPAD), % stem and root lodging (S&RL) among the RILs. Significant positive correlation of GY with BR and SPAD and negative correlation with S&RL indicated the potential use of these secondary traits in selection indices under waterlogged conditions. RILs were genotyped with 331 polymorphic single nucleotide polymorphism (SNP) markers using KASP (Kompetitive Allele Specific PCR) Platform. QTL mapping revealed five QTL on chromosomes 1, 3, 5, 7 and 10, which together explained approximately 30% of phenotypic variance for GY based on evaluation of RIL families under waterlogged conditions, with effects ranging from 520 to 640 kg/ha for individual genomic regions. 13 QTL were identified for various secondary traits associated with waterlogging tolerance, each individually explaining from 3 to 14% of phenotypic variance. Of the 22 candidate genes with known functional domains identified within the physical intervals delimited by the flanking markers of the QTL influencing GY and other secondary traits, six have previously been demonstrated to be associated with anaerobic responses in either maize or other model species. A pair of flanking SNP markers has been identified for each of the QTL and high throughput marker assays were developed to facilitate rapid introgression of waterlogging tolerance in tropical maize breeding programs.

Molecular mapping across three populations reveals a QTL hotspot region on chromosome 3 for secondary traits associated with drought tolerance in tropical maize.

Identifying quantitative trait loci (QTL) of sizeable effects that are expressed in diverse genetic backgrounds across contrasting water regimes particularly for secondary traits can significantly complement the conventional drought tolerance breeding efforts. We evaluated three tropical maize biparental populations under water-stressed and well-watered regimes for drought-related morpho-physiological traits, such as anthesis-silking interval (ASI), ears per plant (EPP), stay-green (SG) and plant-to-ear height ratio (PEH). In general, drought stress reduced the genetic variance of grain yield (GY), while that of morpho-physiological traits remained stable or even increased under drought conditions. We detected consistent genomic regions across different genetic backgrounds that could be target regions for marker-assisted introgression for drought tolerance in maize. A total of 203 QTL for ASI, EPP, SG and PEH were identified under both the water regimes. Meta-QTL analysis across the three populations identified six constitutive genomic regions with a minimum of two overlapping traits. Clusters of QTL were observed on chromosomes 1.06, 3.06, 4.09, 5.05, 7.03 and 10.04/06. Interestingly, a ~8-Mb region delimited in 3.06 harboured QTL for most of the morpho-physiological traits considered in the current study. This region contained two important candidate genes viz., zmm16 (MADS-domain transcription factor) and psbs1 (photosystem II unit) that are responsible for reproductive organ development and photosynthate accumulation, respectively. The genomic regions identified in this study partially explained the association of secondary traits with GY. Flanking single nucleotide polymorphism markers reported herein may be useful in marker-assisted introgression of drought tolerance in tropical maize.

QTL mapping in three tropical maize populations reveals a set of constitutive and adaptive genomic regions for drought tolerance.

Despite numerous published reports of quantitative trait loci (QTL) for drought-related traits, practical applications of such QTL in maize improvement are scarce. Identifying QTL of sizeable effects that express more or less uniformly in diverse genetic backgrounds across contrasting water regimes could significantly complement conventional breeding efforts to improve drought tolerance. We evaluated three tropical bi-parental populations under water-stress (WS) and well-watered (WW) regimes in Mexico, Kenya and Zimbabwe to identify genomic regions responsible for grain yield (GY) and anthesis-silking interval (ASI) across multiple environments and diverse genetic backgrounds. Across the three populations, on average, drought stress reduced GY by more than 50 % and increased ASI by 3.2 days. We identified a total of 83 and 62 QTL through individual environment analyses for GY and ASI, respectively. In each population, most QTL consistently showed up in each water regime. Across the three populations, the phenotypic variance explained by various individual QTL ranged from 2.6 to 17.8 % for GY and 1.7 to 17.8 % for ASI under WS environments and from 5 to 19.5 % for GY under WW environments. Meta-QTL (mQTL) analysis across the three populations and multiple environments identified seven genomic regions for GY and one for ASI, of which six mQTL on chr.1, 4, 5 and 10 for GY were constitutively expressed across WS and WW environments. One mQTL on chr.7 for GY and one on chr.3 for ASI were found to be 'adaptive' to WS conditions. High throughput assays were developed for SNPs that delimit the physical intervals of these mQTL. At most of the QTL, almost equal number of favorable alleles was donated by either of the parents within each cross, thereby demonstrating the potential of drought tolerant × drought tolerant crosses to identify QTL under contrasting water regimes.

Qualidade de sabor de tomates dos tipos salada e cereja e sua relação com caracteres morfoagronômicos dos frutos / Taste quality of salad and cherry tomatoes and their relationship with the morphoagronomic characteristics of the fruits

Frutos no estádio vermelho maduro de trinta e três acessos de tomate do banco de germoplasma do CCA-UFES, sendo 15 do "tipo Cereja" e 18 do "tipo Salada", foram caracterizados com base nos seguintes descritores morfoagronômicos: peso médio do fruto; comprimento médio do fruto; diâmetro médio do fruto; diâmetro da cicatriz peduncular; espessura do mesocarpo do fruto; teor de sólidos solúveis e pH do fruto. Com base nas variáveis teor de sólidos solúveis (TSS) e pH do fruto, calculou-se a variável sabor, por meio da relação TSS/pH². Foram realizadas análises de variâncias e análises de correlações simples e parciais, determinando a distribuição dos acessos quanto às classes de sabor. Com base nas distribuições de frequências, formaram-se quatro classes para essa variável, sendo que, a maior parcela (33 por cento) dos acessos "tipo Salada" alocaram-se na classe mais baixa (0,05-0,12 ºBrix.pH-2), correspondendo a frutos de sabor menos desejável, enquanto a maior parcela (30 por cento) dos acessos "tipo Cereja", alocaram-se em classe imediatamente superior (0,13-0,20 ºBrix.pH-2). Os dados demonstram a possibilidade de se obter ganhos genéticos para sabor concomitantemente ao peso, comprimento e espessura do mesocarpo dos frutos.

Fruits in the ripe red stage of thirty three tomato (Lycopersicon esculentum Mill.) accessions from CCA-UFES germplasm collection, being 15 "Cherry type" and 18 "Salad type", were characterized based on the following morphooagronomic descriptors: average fruit weight; average fruit length; average fruit diameter; peduncle scar diameter; fruit mesocarp thickness; soluble solids and fruit pH. Based on the data from the soluble solids and fruit pH, the flavor variable was calculated by the ratio TSS/pH². Variance analysis and simple and partial correlations were calculated, and the accessions were clustered in flavor classes. Based on the statistical model of distribution of frequencies, four classes were formed for flavor variable. The largest portion (33 percent) of the accessions of salad type were located in the lowest class (0.05-0.12 ºBrix.pH-2), corresponding to the accessions with not so desirable a flavor, while the largest portion (30 percent) of the accessions of the "cherry" type were clustered in the next class above (0.13-0.20 ºBrix.pH-2). The possibility of concomitantly obtaining genetic gains for flavor, weight, length and mesocarp thickness of the fruits was demonstrated.