PISTILLATA (PI)-like genes are crucial regulators of flowering in angiosperms. A homologue of PI, designated as AcPI (Genbank accession number HQ717796), was isolated from pineapple cultivar Comte de Paris by reverse transcriptase polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE). The cDNA sequence of AcPI is 907 bp in length and contains an open reading frame of 594 bp, which encodes a protein of 197 amino acids. The molecular weight was 2.29 kDa and the isoelectric point was 9.28. The alignment showed that AcPI had a high identity with CsPIC2 (78.6%), AoPI (77.4%), OrcPI (75.7%) and HPI2 (72.4%). Quantitative real-time polymerase chain reaction (qRT-PCR) analyses in different tissues showed that the expression pattern of AcPI was different from the B-class genes in eudicots. AcPI was expressed in all the tissues investigated. The expression level was very low in fruit stems, bracts, leaves and sepals, high in petals and carpels, and moderate in apical meristems, flesh and stamens. The qRT-PCR analyses in different stages indicated that the expression of AcPI reached the highest level at 40 days after flower inducement, when the multiple fruit and floral organs were forming. It proved the important role of AcPI in floral organs and fruit development. The 35S::AcPI transgenic Arabidopsis plants flowered earlier and had more inflorescences or branches than wild type plants.

Watercore is a physiological disorder in pineapples, which is expressed as fluid deposition in intercellular spaces and presents as water soaked. This disorder affects the fruit quality and decreases storage life, resulting in enormous commercial losses to growers and restricting the development of the pineapple industry in China. However, the molecular mechanism of watercore remains unclear. In order to elucidate the molecular mechanism of pineapple watercore, the transcriptome analyses of watercored and normal fruits were carried out in pineapples for the first time using de novo RNA-seq technology. High-quality reads of 46.66 and 43.71 M were obtained in the transcriptomes of normal and mildly watercored fruits, respectively. Clean reads of 45.50 and 42.79 M were obtained after filtering the original data. These genes are useful resources in subsequent pineapple watercore research. Fifty genes in phenylpropanoid biosynthesis, glucose metabolism, calcium transport, and cell wall metabolism were considerably different between normal and watercored fruits. Among them, the expressions of the AcPME, AcBGLU43, Ac4CL5, AcPER1, and AcPOD genes were upregulated by 7–21 times in watercored fruit, while the expressions of AcSUS7 were downregulated by 16.61 times, and the expressions of other differential genes were upregulated or downregulated by more than 2 times. A total of 38 differentially expressed transcription factors were obtained by screening. Among these transcription factors, WRKY was the most abundant, followed by MYB. The acquisition of these genes is important for the first understanding of the molecular mechanism of this physiological disorder.

Pineapple (Ananas comosus) is an economically important tropical fruit in Guangdong Province, China. The plants were seriously infected with a year-round leaf spot disease. During September to November 2022, the leaf spot disease of pineapple was found in Xuwen city and Zhanjiang city of Guangdong Province. A disease survey of 1 ha revealed that pineapple was affected at an incidence ranging from 30% to 50%. The disease caused economic loss to control plant diseases with chemicals. The initial symptoms were observed after 1 month of planting in October and included yellow spot and developed brown necrotic lesions. The leaves of pineapples showed symptoms of Large brown necrotic lesions appear on leaves especially on the tip of basal leaves. The diseased leaves were collected and surface-disinfested in 1% NaClO for 2-3 m, rinsed with sterilized water, air dried, placed on potato dextrose agar (PDA) medium, and incubated for 3 to 5 days at 28°C. Two isolates (PLF1 and PLF2) were collected and purified using the single-spore method. Colonies developing on PDA were in a circle with abundant white, densely fluffy aerial mycelium, pale to colorless after 3 d and pale orange 5-15 d later. Cultures of the isolates produced macroconidia which were falcate, 1-3-septate, hyaline, 18.2-43.4×4.8-6.8 µm(n=50). Cultures of the isolate also produced large amount of conidia which were hyaline, oblong, no septate, 5.2-10.6×2.7-5.2 µm (n=50). These characteristics were consistent with the description of Fusarium sp. (Chitrampalam et al. 2018). For molecular identification, the genomic DNA of the 2 isolates was extracted. The fragments of internal transcribed spacer (ITS), translation elongation factor 1α (EF1α) and β-tubulin were amplified and sequened using the primer pairs of ITS4/ITS5, EF1/EF2 (O'Donnell et al. 2008) and T1/T2 (O'Donnell et al. 1997). These sequences were deposited in GenBank (OR501466, OR501467 for the ITS; OR499874, OR499875 for elongation factor; OR499876, OR499877 for β-tubulin). Phylogenetic trees were constructed in MAGA 11 using the Maximum likelihood (ML) method based on the concatenated sequences of ITS, EF1α, and Tublin (Figure 1). The 2 isolates were grouped with F. solani A01-1 (GCA_027945525.1) with a bootstrap value of 100 in the phylogenetic tree. The morphology and multi-gene phylogenetic analysis indicated that the new isolates are F. solani. The 2 isolates were selected for pathogenicity tests to fulfill Koch's postulates. Six plants at seven- to ten-leaf stage were inoculated with each isolate separately. Three sites of each leaf were wounded with a sterile needle and covered with a piece of cotton drenched with 200 µl spore suspension (107 spores/ml) from each isolate cultured in PD medium. Leaves inoculated with PD medium served as negative controls. Inoculated plants were placed in an incubator at 28°C, and 80% humidity under a 12-h light/dark cycle for 7 days. After 7 days of incubation, necrotic spots were observed in all the inoculated plants except the negative control. The pathogenicity tests were conducted three times with similar results. The strains were then reisolated from the lesions and found to be Fusarium solani as those of the inoculum. F．ananatum， F. guttiforme and F. subglutinans have been reported to infect all parts of pineapplefusariosis disease (Jacobs et al. 2010; Stępień et al. 2013; Ventura et al. 1993). To our knowledge, this is the first report of fusariosis on Pineapple caused by F. solani. Identification of F. solani as a disease agent on pineapple will assist in disease management for this important fruit tree.

Breeding is an effective method for the varietal development of pineapple. However, due to open pollination, it is necessary to conduct authentic identification of the hybrid offspring. In this study, we identified the authenticity of offspring and analyzed the genetic diversity within the offspring F₁ hybrids resulting from crosses between ‘Josapine’ and ‘MD2’ by single nucleotide polymorphism (SNP) markers. From the resequencing data, 26 homozygous loci that differentiate between the parents have been identified. Then, genotyping was performed on both the parents and 36 offspring to select SNP markers that are suitable for authentic identification. The genotyping results revealed that 2 sets of SNP primers, namely SNP4010 and SNP22550, successfully identified 395 authentic hybrids out of 451 hybrid offspring. We randomly selected two true hybrids and four pseudohybrids for sequencing validation, and the results have shown that two true hybrids had double peaks with A/G, while pseudohybrids had single peaks with base A or G. Further study showed that the identification based on SNP molecular markers remained consistent with the morphological identification results in the field, with a true hybridization rate of 87.58%. K-means clustering and UPGMA tree analysis revealed that the hybrid offspring could be categorized into two groups. Among them, 68.5% of offspring aggregated with MD2, while 31.95% were grouped with Josapine. The successful application of SNP marker to identify pineapple F₁ hybrid populations provides a theoretical foundation and practical reference for the future development of rapid SNP marker-based methods for pineapple hybrid authenticity and purity testing.

Pineapple (Ananas comosus) is a perennial economically important tropical fruit in Guangxi Province, China. Between September to November 2022, the rot of heart leaves of pineapple was found on 6.7 hectares of pineapple, NaLang village Jiangxi Town, Jiangnan District, Nanning City and on 200 hectare Liutian Village, Wangmao Town, Bobai County, Yulin City. The disease incidence of the investigated 10500 plants was from 20% to 30%. The basal heart leaves near the soil surface showed symptoms of water-soaked lesions and soft rot. The infected heart leaves were easily pulled out. As the disease developed, 800 plants of the investigated diseased plants collapsed and died. The diseased leaves from each district were surface-disinfected for 3 min with 1.0% hypochlorite solution, then rinsed three times in sterile water, and plated to carrot agar medium (CA media) (Luo et al. 2012). Inoculated dishes were incubated at 28°C in the dark. After 5 days, Eight mycelium colonies were recovered from diseased tissue. Colonies developing on CA exhibited white cottony mycelium which was aseptate. Numerous sporangia and chlamydospores were visible after 10-15 d later. The chlamydospores were spherical in shape and measured an average of 25.8 to 37.5 μm. The shape of the sporangia was papillate, oval or spherical, and 34.5 to 58.2 μm. These characteristics were consistent with the description of Phytophthora (Stamps et al. 1990). For molecular identification, the direct colony PCR method (Lu et al. 2012) was used to amplify the ITS of rDNA, β-tubulin (Tu), and elongation factor (EF) locus of the 2 strains NNPN1 from Nanning city and YLPN1 from Yulin city using the primer pairs of ITS4/ITS5, T1/T2 (O'Donnell et al. 1997) and EF1/EF2 (O'Donnell et al. 1998). The resulting sequences were deposited in GenBank (OR612028 and OR612029 for ITS; OR620158 and OR620159 for elongation factor; OR620160 and OR620161 for β-tubulin). BLAST searches with the three gene sequences revealed the greatest similarity with the sequences of some Phytophthora sp. The complete genome sequences of highly similar Phytophthora sp. were downloaded and the sequences of the corresponding 3 genes of each genome was extracted by Bioedit software. Phylogenetic trees were constructed in MEGA 11 using the maximum likelihood (ML) method based on the concatenated sequences of ITS, EF1α, and Tubulin (Figure 1). The 2 isolates grouped with P. nicotianae in the phylogenetic tree. The morphology and multi-gene phylogenetic analysis indicated that the new isolate was P. nicotianae. Tests of pathogenicity were performed according to Koch's postulates using the P. nicotianae strains NNPN1 and YLPN1. Fresh wounds were made symmetrically with a sterile needle on 2 tender basal leaves of pineapple plants (Bali variety) at the 8- to 10-leaf stage and each wound was covered with a piece of mycelium disc from each isolate. Control seedlings were inoculated identically except CA medium disc was used to cover the wound. Plants were placed in pots in a greenhouse at 28°C and 90% relative humidity. After 12 days, soft rot was observed clearly on the base of heart leaves of 9 inoculated plants, while the 9 control plants appeared normal. The pathogenicity tests were conducted three times with similar results. The strains were then reisolated from the infected plants and found to be Phytophthora sp. as those of the inoculum by morphology. P. nicotianae was previously reported as the causal agent of heart rot of pineapple in Guangdong and Hainan Province of China (Luo et al. 2012; Shen et al. 2013). To our knowledge, this is the first report of P. nicotianae on pineapple in Guangxi province in China. Identification of the pathogen of heart rot disease on pineapple is vital to reduce yield losses of the disease using effective control method.