Detection of Chromosomal Regions for Male Sterility in the Cultivated Strawberry <i>Fragaria</i> × <i>ananassa</i> Duch.

Abstract

Male sterility is defined as the loss of pollen fertility, and it represents a plant reproductive isolation symptom, along with self-incompatibility. It plays an important role in the efficient production of F 1-hybrid seeds, which results in affordable seed prices for farmers. Male sterile cultivated strawberry Fragaria × ananassa Duch. plants were found in an F 1 population and reciprocal backcrossed populations derived from a cross between 'Fukuoka S6' and 'Kaorino'. Male sterile plants were clearly distinguished from male fertile plants in those populations based on the anther color. The pollen of the male sterile plants was a lighter yellow color and not maturely shaped compared with pollen of male fertile plants. Genotyping was performed using EST-SSR markers in the three populations. Quantitative trait locus analyses for pollen fertility were conducted independently using three kinds of populations, and this revealed that male sterility was controlled by three independent chromosomal regions in these populations, which corresponded to chromosome 4 in the wild strawberry (Fragaria vesca) genome. One region was derived from 'Fukuoka S6' and the other two regions from 'Kaorino'. The segregation patterns of fertile and sterile plants in each population clearly supported the three gene theory of male sterility in cultivated strawberries. The accumulation of recessive alleles at the three regions led to male sterility, and the existence of a dominant allele in at least one region resulted in fertile pollen. Male sterile plants were also found in two self-pollenated populations derived from 'Fukuoka S6' and 'Kaorino', and the effects of the three regions were validated. The adaptability levels of the three genes with different genetic backgrounds were also evaluated using core collection cultivars and selected lines derived using recurrent selection. We also detected flanking DNA markers for the three regions associated with male sterility. The use of these markers, which are in the vicinity of quantitative trait loci and responsible for malesterility, could increase the efficiency of producing seed-propagated strawberry F 1-hybrids.

Comparative QTL mapping for male sterility of cultivated strawberry (<i>Fragaria</i> × <i>ananassa</i> Duch.) using different reference genome sequences

“…(1) qMS4.1 : The S 2 population of ‘Fukuoka S6’ was used. As we revealed previously ( Wada et al 2020 ), ‘Fukuoka S6’ harbors two heterozygous alleles (in QTL regions qMS4.1 and qMS4.2 ) and a recessive homozygous allele (in QTL region qMS4.3 ). In the DNA marker-assisted selection (MAS) conducted here, we used the SSR marker FVES1264 for genotyping of qMS4.1 and FVES1356 for qMS4.2 , both of which were developed by Isobe et al (2013) and selected as flanking markers for the two QTLs ( Wada et al 2020 ).…”

“…As we revealed previously ( Wada et al 2020 ), ‘Fukuoka S6’ harbors two heterozygous alleles (in QTL regions qMS4.1 and qMS4.2 ) and a recessive homozygous allele (in QTL region qMS4.3 ). In the DNA marker-assisted selection (MAS) conducted here, we used the SSR marker FVES1264 for genotyping of qMS4.1 and FVES1356 for qMS4.2 , both of which were developed by Isobe et al (2013) and selected as flanking markers for the two QTLs ( Wada et al 2020 ). Before selecting S 2 plants, we selected S 1 plants derived from self-pollination of ‘Fukuoka S6’, which harbored a heterozygous allele in qMS4.1 and a recessive allele in qMS4.2 , and conducted self-pollination of the relevant S 1 plant to obtain S 2 seeds.…”

“…Before selecting S 2 plants, we selected S 1 plants derived from self-pollination of ‘Fukuoka S6’, which harbored a heterozygous allele in qMS4.1 and a recessive allele in qMS4.2 , and conducted self-pollination of the relevant S 1 plant to obtain S 2 seeds. From the S 2 population, we further selected 20 male-fertile and 20 male-sterile plants in the following manner: We grew 200 plants in a greenhouse and confirmed their male fertility or sterility at anthesis by anther color ( Wada et al 2020 ). From the male-fertile plants, we used MAS to select “perfect” male-fertile plants that carried dominant homozygote alleles and whose self-pollinated progeny did not include male-sterile plants.…”

“…The objective of this study was to map the three QTLs for male sterility that were identified by Wada et al (2020) in two strawberry reference genome sequences on different reference maps ('Camarosa' and 'Reikou') of the cultivated strawberry genome (Edger et al 2019b(Edger et al , https://www. biorxiv.org/content/10.1101(Edger et al /2021.…”

“…In our previous research, we performed QTL analysis using expressed sequence tag-simple sequence repeat (EST-SSR) markers ( Isobe et al 2013 ) and identified three independent quantitative traits loci (QTLs) for male sterility of cultivated strawberry ( Wada et al 2020 ). We also revealed that the accumulation of recessive alleles of the three QTLs induced male sterility ( Wada et al 2020 ) and all the primer sequences of the flanking SSR markers for the three QTLs were estimated to be derived from Fvb4 of the diploid F. vesca genome ( Shulaev et al 2011 , Tennessen et al 2013 ). Although our previous study was the first report of male sterility of cultivated strawberry, F. × ananassa ssp.…”