The number of petals in a flower is one of the most important appearance qualities of ornamental flowers. In Eustoma, the number of petals fluctuates significantly and little is known about how it is controlled. We investigated the cultivating conditions that affect the number of petals in double flowers and tried to develop a technique for growing splendid corolla. High temperature in the reproductive phase reduces the number of petals. The transient treatment of high temperature just prior to the petal initiation stage is sufficient to control such a reduction. The measurement of flower bud growth showed that one week of temperature treatment is necessary to control the number of petals in a flower. The integration of our results demonstrated that both daytime and nighttime temperatures affected the number of petals and that the number of petals was clearly correlated with average daily temperature within the range of 20°C < x < 25°C. This phenomenon applies to various cultivars in Eustoma grandiflorum. We propose the greenhouse conditions necessary to achieve both high quality flowers and reduced energy consumption by considering the temperature and stages of flower development.

Lisianthus (Eustoma grandiflorum) is an important floricultural crop cultivated worldwide. Despite its commercial importance, few DNA markers are available for molecular genetic research. In this study, we constructed a genetic linkage map and to detect quantitative trait loci (QTLs) for important agronomic traits of lisianthus. To develop simple sequence repeat (SSR) markers, we used 454-pyrosequencing technology to obtain genomic shotgun sequences and subsequently identified 8263 putative SSRs. A total of 3990 primer pairs were designed in silico and 1189 unique primer pairs were extracted through a BLAST search. Amplification was successful for more than 1000 primer pairs, and ultimately 278 SSR markers exhibited polymorphism between the two lisianthus accessions evaluated. Based on these markers, a genetic linkage map was constructed using a breeding population derived from crosses between the two accessions, for which flowering time differed (>140 days when grown under 20°C). We detected one QTL associated with flowering time (phenotypic variance, 27%; LOD value, 3.7). The SSR marker located at this QTL may account for variation in flowering time among accessions (i.e., three accessions whose nodes of the first flower were over 30 had late-flowering alleles of this QTL).

Fusarium root rot of lisianthus (Eustoma grandiflorum) caused by Fusarium solani is one of the most important and damaging lisianthus diseases. It occurs commonly in Japan and worldwide and causes serious crop losses. However, little effort has been made to breed lisianthus for resistance to this disease. We initiated a breeding program for resistance to F. solani in 2014. Twenty-nine lisianthus cultivars (E. grandiflorum) and one inbred line of Eustoma exaltatum were evaluated for resistance to two isolates (MAFF712388 and MAFF712411) of F. solani, as a first step toward the breeding of resistant cultivars. Seedlings were inoculated following injury by needle, then grown using hydroponic equipment-an efficient and reliable method for evaluating resistance. We found large differences in resistance among the 29 cultivars and the one inbred line tested. 'Papillon Pink Flash' was highly resistant to both isolates and showed no disease symptoms in a total of four tests. Furthermore, E. exaltatum Ohkawa No. 1 was highly resistant to isolate MAFF712388, showing no disease symptoms, and resistant to isolate MAFF712411. On the other hand, 'Mink', 'Nagisa A', 'Nagisa B', and 'Vulcan Marine' were stably susceptible with 70% to 100% of plants of these four cultivars wilting in all tests. MAFF712411 had greater pathogenicity than MAFF712388, but it is not clear whether the two isolates belong to different races.

Flower-bud blasting is a constraint for producing Eustoma grandiflorum so a preventative strategy is needed. Flower-bud blasting occurs under low light intensity and high fertilizer input. To gain insight into the mechanisms of flower-bud blasting, we conducted a detailed characterization of flower development under normal and blastinducing conditions. We found that floral buds under low light intensity ceased to grow at the stamen and gynoecium differentiation stages, although sepals and petals were initiated normally. Aborted flowers rarely had normal ovules. Moreover, an expanded apical meristem was observed. These results show that the differentiation and development of reproductive organs are critically suppressed by blast-inducing conditions; however, combined application of 300 ppm benzylaminopurine and 200 ppm gibberellic acid-3 to floral buds resulted in about five-fold greater frequency of flower opening compared to controls. Blasting inhibition also resulted from excising the inflorescent branch, suggesting the decrease in assimilates in flower buds would be attributed to flower-bud blasting. Moreover, hormone application combined with excision had an additive effect for preventing flower-bud blasting, suggesting that these treatments independently inhibit flower-bud blasting. These results suggest that flower-bud blasting in Eustoma is a break in floral development around the stamen and gynoecium initiation stages and is integrally induced by the factors related to hormone biosynthesis and the decrease in assimilates.

Inflorescence refers to the spatial and temporal patterns of flowers and analysis of the branching pattern would facilitate understanding of the entire structure of inflorescence. To gain an insight into the inflorescence architecture of Eustoma, the popularity of which has soared worldwide, we conducted a detailed characterization of inflorescence development. In particular, we focused on identifying meristem types and describing their development, both of which may affect the inflorescence structure. During reproductive development, the shoot apical meristem usually splits into two meristems, either or both of which can become inflorescence meristems and capable of producing a floral meristem. However, the inflorescence meristems ultimately abort flower production. Meanwhile, axillary meristems sometimes grow and convert into inflorescence meristems, leading to differentiation of floral meristems. Hence, different types of inflorescence result from different types of meristem, and changes in meristem activity. We elucidated the factors influencing inflorescence structure and classified them into eight groups.