Characteristics and inheritance of natural facultative-parthenocarpic fruit-set in ‘Nadja’ tomato under low temperature conditions

‘Nadja’ tomato (Lycopersicon esculentum Mill.) set both seedless and seeded fruits under the fluctuating temperatures prevailing during late-March and early-April in Assiut district, Egypt. Entirely seedless fruits developed under the low temperatures prevailing during Dec. Seedless fruits seemed to develop vegetatively , i.e. with no need for stimulus pollination. All seedless fruits were normally jelled and appeared similar in shape and size to the seeded fruits. Study of F₁, F₂, and backcross generations for the crosses ‘Cal Ace’ × ‘Nadja’ and ‘Peto-86’ × ‘Nadja’ suggested that the expression of the trait was due to single homozygous recessive gene. Yield produced by ‘Nadja’ was higher than the F₁, F₂, and backcross generations in both the early- summer and the late-winter plantings. Potentially useful parthenocarpic segregates were found in F₂ of the two crosses for increased fruit weight of normally shaped and jelled fruits. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetics of parthenocarpy in tomato under a low temperature regime: II Cultivar ‘Severianin’

Summary Genetics of parthenocarpy in cv Severianin was tested under natural low-temperature conditions under which only seedless fruits were produced. Results were consistent with the hypothesis that two recessive genes are involved in the expression of parthenocarpy under low-temperature conditions. One gene, pat-2, has major effects on the expression of parthenocarpy. A second gene, mp, in the homozygous form, influences expression of pat-2 in both the homozygous and heterozygous conformation and may be present in non parthenocarpic phenotypes. Linkage tests, using 26 morphological marker genes, located pat-2 between solanifolia, sf (chromosome 3 site 111) and baby-lea syndrome, bls (chromosome 3 L site 74) close to sf. The location of the minor gene for parthenocarpy, mp, was not detected.     

Effect of hot water treatments on chilling injury and expression of a new C-repeat binding factor (CBF) in ‘Hongyang’ kiwifruit during low temperature storage

Kiwifruit is cold-sensitive and very susceptible to chilling injury (CI) during low temperature storage. In this study, kiwifruit (Actinidia chinensis cv. Hongyang) were pre-treated by water dip for 10 min at 20 (control) or 35, 45, or 55 °C (heat pretreatments) and then stored at 0 °C for 90 days to investigate the effect of hot water treatments (HWT) on chilling injury tolerance. Results showed that 35 °C and 45 °C HWT alleviated but did not completely prevent chilling injury development. By contrast, 55 °C HWT increased symptoms of chilling injury. The 45 °C HWT was the most effective at reducing chilling injury index and incidence. Compared with the other HWT, fruit treated at 45 °C exhibited higher firmness and soluble solids content (SSC), and lower malondialdehyde (MDA) content, lipoxygenase (LOX) activity and ethylene production rate. C-repeat/dehydration-responsive element binding factors (CBFs) are key regulators in cold response. To investigate the molecular regulation of HWT on chilling tolerance of kiwifruit, a 637 bp CBF gene was identified and the relative expression of AcCBF was measured by RT-qPCR. In accordance with the effects of HWT on physiological parameters of chilling injury, AcCBF expression level was highest in the 45 °C HWT. These results indicate that HWT at 45 °C for 10 min prior to low temperature storage is effective for alleviating symptoms of chilling injury in ‘Hongyang’ kiwifruit.     

Identification of a novel gene (Apq1) from the indica rice cultivar ‘Habataki’ that improves the quality of grains produced under high temperature stress

The appearance of brown rice grown under high temperature conditions is an important characteristic for improvement in Japanese rice breeding programs. We performed a QTL analysis of the appearance quality of brown rice using chromosome segment substitution lines of the indica cultivar ‘Habataki’ in the ‘Koshihikari’ genetic background. A line carrying a ‘Habataki’ segment on chromosome 7 showed a high percentage of perfect grains produced under high temperature conditions during the ripening period. To verify the role of this segment, and to narrow down the region containing the useful allele, substitution mapping was performed using multiple paired lines. As a result, the chromosomal location of a gene that we named Appearance quality of brown rice 1 (Apq1) was delimited to a 48-kb region. In addition, we developed an Apq1-near isogenic line (NIL) to evaluate the effect of Apq1 on various agronomic traits. Under high temperature conditions during the ripening period, the Apq1-NIL produced significantly higher percentages of perfect grains than ‘Koshihikari’. Other agronomic traits, including yield and palatability, were similar between the Apq1-NIL and ‘Koshihikari’. Therefore, the ‘Habataki’ allele of Apq1 will be useful in breeding programs aimed at improving the quality of grains ripened under high temperature conditions.