Daylily (Hemerocallis spp.) are perennial herbaceous flowers with high ornamental and medicinal value. Currently, the breeding of new daylily cultivars was mainly achieved through hybrid breeding, but issues such as self-incompatibility, hybridization barriers, and asynchronous reproductive phenology severely hinder the breeding process. Understanding pollen viability was essential for daylily breeding and cultivar improvement. In this study, we systematically investigated the effects of pollen viability determination methods, collection time, medium combinations, culture temperature and storage conditions on the pollen germination characteristics of daylily, using five daylily cultivars introduced in the Zhanjiang region of China as materials. Comparing the Iodine-potassium iodide (I₂-KI) staining and Acetocarmine staining, the results of 2,3,5-Triphenyltetrazolium Chloride (TTC) staining showed a significant positive correlation (p < 0.05) with the in vitro germination rate, which is suitable for the rapid detection of daylily pollen vigor. The daylily variation of pollen vigor was significant in different cultivars, and most cultivars had the highest vigor at 9:00–12:00 a.m., which was suitable for artificial pollination. The in vitro germination experiment showed that sucrose concentration was the key factor for daylily pollen germination and pollen tube growth, and the optimal medium for pollen in vitro germination was 50 g/L⁻¹ sucrose + 0.1 g/L⁻¹ H₃BO₃ + 0.06 g/L⁻¹ KNO₃ + 0.2 g/L⁻¹ Ca(NO₃)₂. The temperature experiment showed that the optimum temperature for pollen germination was 24.1–26.7 °C, and the optimum range for pollen tube growth was 24.1–25.7 °C, and the high temperature significantly inhibited the elongation rate of pollen tube. Storage experiments showed that low temperature (−40 °C) combined with drying treatment could significantly prolong pollen life, and the “Water Dragon” variety still maintained 41.29% vigor after 60 days of dry storage. This study provides theoretical basis and technical support for the introduction and domestication of daylily in South China, hybridization and garden application.

Drought stress is one of the key abiotic stress factors limiting the growth and development, yield formation, and improvement in the quality of jackfruit (Artocarpus heterophyllus). However, systematic evaluations of drought tolerance in jackfruit germplasm resources remain limited. In this study, six jackfruit cultivars were used as materials. By systematically comparing 26 indicators, including leaf structural characteristics, chlorophyll concentration, and photosynthetic parameters, the primary evaluation indicators for jackfruit drought tolerance were identified, and clear microscopic structural images of leaves from different jackfruit cultivars were obtained. In this study, significant differences were observed among different jackfruit germplasm resources in terms of leaf structure, chlorophyll concentration, and photosynthetic characteristics. Comprehensive analysis identified A. ‘Changyou’ as the jackfruit cultivar with the highest drought tolerance score and A. ‘Siji’ as the variety with the lowest drought tolerance score. By establishing a systematic evaluation system for jackfruit drought tolerance, it was found that jackfruit cultivars with high drought tolerance had significantly thicker palisade parenchyma than other cultivars, a rougher leaf epidermis, and more densely distributed stomata on the leaves, while their chlorophyll concentration was significantly lower than that of cultivars with lower drought tolerance scores. Jackfruit cultivars with the lowest drought resistance scores had significantly lower net photosynthetic rates, transpiration rates, stomatal conductance, and light saturation points than other cultivars. This study’s results established a drought resistance evaluation system for jackfruit germplasm resources, providing theoretical support for the selection and breeding of high-drought-resistant superior jackfruit cultivars.

Jackfruit (Artocarpus heterophyllus) is a tree of the Moraceae family and widely cultivated due to its fruit with diverse medicinal and nutritional properties in China. In June 2022, a serious bark cracking disease was observed on jackfruit in the 2400-acre orchards of Hekou, Yunnan (E103°52'39″ N22°34'14″). The disease mainly harms tree trunks and branches. The incidence rates were about 90% and the mortality rate of plants reached up to 50%. Symptoms initially appeared as small watered-spots with gumming. Subsequently the bark rotted and cracked, the xylem gradually turned brown (Figure 1). Ultimately, the upper branches of infected parts withered and died. Small 5×5 mm segments of infected tissue from 50 randomly selected trunk with typical symptoms were surface sterilized with 75% alcohol solution and 3% hydrogen peroxide solution respectively, rinsed three times with sterile water, and placed onto PDA medium with 50mg/L of penicillin. The plates were kept at 25 to 28 ℃ in the dark. Fusarium-like colonies were consistently isolated on potato dextrose agar (PDA) and 15 monoconidial isolates were obtained. On PDA, colonies exhibited white and fluffy aerial mycelia. Main hyphae are up to 5.5 µm wide. The microconidia were hyaline, falcate, measuring 4.50-9.00×2.30-4.00 µm (av.6.50×3.15 µm, n=50). Macroconidia with septation were 9.00-11.50×3.05-5.25 µm (av.10.50×4.15 µm, n=50) with foot-shaped basal cells, tapering to hooked apical cells (Figure 2). These morphological characterizations were similar to Fusarium sp. (Sun et al, 2018). For further identification, the internal transcribed spacer (ITS) region, RNA polymerase II subunit (RPB2) and translation elongation factor 1-alpha (tef1) genes sequence of isolate BLM1 and BLM2 were amplified and sequenced with primer pairs of ITS1/ITS4, RPB2-5F2/RPB2-7CR, EF-1/EF-728R respectively (Weir et al, 2012), The sequences were submitted to GenBank (ITS: PQ394640 and PQ394641, RPB2: PQ416997 and PQ416998, TEF: PQ416999 and PQ417000). Blast results showed the sequences of BLM1 and BLM2 had high identity to these of Neocosmospora pseudensiformis (Anamorp: Fusarium pseudensiformis) ex-type CBS 125729 (NRRL 46517) (ITS: 548/553(99%); TEF: 456/466(98%); RPB2: 823/823(100%)) (Sandoval-Denis, et al 2019). Polyphasic identification showed above 98% sequence similarity to N. pseudensiformis CBS 125729, CBS 130.78, NRRL22354, LC13838 (https://www.fusarium.org/Poly%20ID%20Fusarium). Phylogenetic analysis using MEGA 7 based on the combined ITS-TEF-RPB2 sequence data, employing the maximum likelihood (ML) method for the multi-locus dataset, showed that BLM1 and BLM2 clustered with F. pseudensiformis (Figure 3). Two five-year-old healthy Jackfruit trees and ten one-year-old seedlings were used for a pathogenicity test. Three plants were inoculated with PDA medium or with sterile water as an experimental control. The seedlings were cultured in a greenhouse (25℃, 70% relative humidity, 12 h light and dark cycle) and the trees cultured in the field, and the experiment was repeated three times. The inoculation sites on trunk were rinsed with sterile water, surface disinfected with alcohol, slightly wounded with sterilized needles, and inoculate fungal masses containing mycelium and spores, as well as 10 µL of spore suspension (1 × 105 conidia/ml). Seven days after inoculation, white slurry effluent as well as minor cracking and rotting of the trunks were observed on the trunks, whereas no symptoms were observed on the trunks of the controls. The pathogen was reisolated and identified by sequencing the ITS, TEF, and RPB2 genes as being consistent with the original isolates N. pseudensiformis has been reported as a pathogen of fruit rot on Passiflora edulis (Pereira et al, 2019), and this is the first report causing bark cracking on A. heterophyllus in China as well as worldwide. Bark cracking disease had seriously affected jackfruit cultivation, and the report provides an knowledge for the prevention and control of this disease.