The alkaloid content of different samples in different seasons and different developmental stages of MHLC of two tea varieties, Nongdao Yecha (MHLC) and Yunkang 10 (YK10) was determined by HPLC. Caffeine synthase 1 gene (TCS1) was cloned from the cDNA of tea plant by RT-PCR in different samples, and its expression level was analyzed. The results showed that MHLC was a natural tea germplasm resource with low caffeine and high theobromine. Theobromine content of MHLC in different seasons was greater than 23.00 mg/g, while the caffeine content was less than 4.00 mg/g. In addition, the accumulation of caffeine and theobromine in MHLC shoots was the highest, and the leaves at the same stage had higher caffeine and theobromine than stems, and the caffeine and theobromine in leaves and stems gradually decreased with the increase of maturity. Through gene cloning and quantitative analysis, it was found that MHLC had two TCS1 allelic variants: TCS1b (with only theobromine synthase activity) and TCS1d (with both theobromine and caffeine synthase activities). Among them, the high expression of TCS1b and the extremely low expression of TCS1d are likely to be the key reasons for MHLC high theobromine and low caffeine. This research would provide material for low-caffeine tea breeding and molecular basis for the efficient utilization of MHLC.

Virus disease is one of the most serious diseases in tomato production in Hainan, China. The small RNA deep sequencing data of tomato virome in Hainan revealed the presence of Southern tomato virus (STV) in samples from several regions, and a single STV infected sample was found. RT-PCR screening of 987 field samples with virus-like symptoms collected from 2015 to 2021, was carried out to determine the distribution of STV in Hainan province. Results indicated that STV was detected in 142 samples from nine regions, STV had existed in Hainan tomatoes as early as 2015, STV detection rate increased from 8.82% in 2015 to 22.45% in 2021, showing an upward trend year by year. The complete genome length of four isolates amplified using RT-PCR and RACE was identical, each consisting of 3446 nt. Two partially overlapping open reading frames (ORFs) presented in the positive-sense RNA strand, the 5′-proximal ORF (position 147-1280 nt) encoded a 377 amino acid (aa) peptide representing a potential coat protein (p42), the second ORF (position 1048-3336 nt) contained typical motifs for an RNA-dependent RNA polymerase (762 aa). The length of 5′ untranslated region (UTR) and 3′ UTR was 146 nt and 110 nt respectively. Paired comparison showed that the nucleotide similarity among four STV isolates was 99.86%-100.00%, the nucleotide similarities with other STV isolates available in GenBank were 98.45%-99.94%. In phylogenetic trees based on the complete genome of STV, eighty STV isolates were obviously divided into two groups (Group Ⅰ and Group Ⅱ). Group Ⅰ included Asian, American, European and African isolates. In group Ⅱ, except for one Asian isolate, the others were European isolates, and four Hainan isolates were divided into group Ⅰ. The grouping of STV isolates was related to geographical location, may not be related to the host. The regions with high genomic sequence variability between Hainan isolates and group Ⅰ isolates were 881-1061 nt and 1521-1721 nt, and the regions with high genomic sequence variability between Hainan isolate and group Ⅱ isolate were 2041-2241 nt and 2761-2921 nt. No recombination events were found between STV isolates. This is the first report of STV in Hainan Province. The findings of this study would provide an important basis for understanding the distribution and occurrence trends of STV in Hainan province and for the development of effective surveillance and control measure.

There are about 69 species of Mangifera in the world, and 8 species are mainly distributed in China. The long history of mango cultivation in China has resulted in many natural hybrids with local characteristics. In the process of continuous coordinated development with the environment, the appearance of mango, such as branches, leaves and fruits, has changed to some extent, but its pollen has formed unique morphological characteristics while maintaining genetic conservatism and stability. In order to further study the taxonomic significance of the pollen morphology of mango plants and clarify the phylogenetic relationship between mango natural hybrids, this study carried out palynological research and genetic relationship analysis on mango germplasm based on the microscopic characteristics of pollen, and observed the pollen morphology and pollen exine ornamentation of 32 mango materials from two species of mango using scanning electron microscopy. On this basis, cluster analysis was carried out on six quantitative characters of pollen. The results showed that the pollen of 32 the mango germplasms belonged to N3P4C5 type. The polar view was 3-split triangle, and the red view was nearly elliptical. There were three germination grooves, which almost reached both ends; There were differences in the shape and size of pollen, the width of germination ridge, pollen ornamentation, the density and size of pollen outer wall mesh among the materials. Stripes or reticular ornamentation and pits were all over the surface of pollen grains. Most mango pollen belongs to reticular ornamentation. Mesh shapes were diverse, mainly circular and long, with rough ridges. Mesh distribution density varied among different materials. According to the cluster analysis of quantitative characters such as pollen grain size, pollen morphology, germination ridge width, mesh size and mesh density, the 32 mango germplasms could be divided into three groups when the similarity distance was 15. Mango resources from Southeast Asia, such as Machesu M. indica, Siam Mango M. indica, Ren He Carabao M. indica, were clustered into one group in the pedigree map, showing certain regional characteristics; Yun Nan Tu Mango M. indica, Bruce Mango M. indica and Amemwins No.26 M. indica with narrow germination ridge were divided into one type; M. persiciformis, collected M. persiciformis and common domestic M. indica. cultivation species were grouped into one group. The original wild species, Bai Hua M. indica, was grouped with No.1 M. persiciformis, No.2 M. persiciformis, No.3 M. persiciformis, and No.4 M. persiciformis. The resource had the characteristics of primitive and wild types. This study would provide palynological basis for the classification, genetic relationship and evolution of mango pollen morphology.

Scientific evaluation of sugarcane germplasm resources can provide high quality parental materials for sugarcane cross breeding. In this study, seven phenotypic traits of 141 excellent sugarcane germplasm were evaluated for diversity using methods such as principal component analysis and cluster analysis. The variation coefficients of smut rate, cane yield, millable stalks, stalk weight and sucrose content were all greater than 10%, with the variation coefficients of smut rate being the largest at 67.21%. Correlation analysis showed that the cane yield was highly significantly positively correlated with plant height, stalk diameter, millable stalks and stalk weight, and the stalk diameter was highly significantly negatively correlated with millable stalks, and the sucrose content was highly significantly negatively correlated with smut rate. The results of principal component analysis showed that the cumulative contribution rate of 3 principal component factors was 74.725%, among which the first principal component was related to yield traits, the second principal component was related to stems and quality traits, the third principal component was related to disease traits and quality traits. Based on cluster analysis, the 141 sugarcane germplasm resources could be divided into 3 groups, among which group Ⅰ had the taller plants, highest yield and highest sucrose content, highest disease resistance, strong persisrence, and had excellent performance for all traits. Group Ⅱ had the smaller plants, lowest yield and lowest sucrose content, lowest disease resistance, poor persisrence, and had poor performance for all traits. Group Ⅲ had average performance for all traits. 60 germplasm resources were selected with excellent overall performance by principal compoment analysis results and cluster analysis results, among which ZZ153303, ZZ150505, ZZ165201 and ZZ151106 could be used as high sugar content parents, ZZ15710, ZZ160913, ZZ162026, ZZ112819, ZZ1415219, ZZ1510055, ZZ140802 and ZZ151106 could be used as highly resistant smut parents, ZZ134007, ZZ118607, ZZ167010, ZZ144101 and ZZ156615 could be used as high yield parents.

With the development of the aerospace industry, the method of combining traditional breeding technology with aerospace mutagenesis technology to achieve breeding goals has been widely recognized by breeding experts. The problems faced by the scale of the banana industry in Fujian make the breeding of new banana varieties an important issue. In the early stage of this study, Brazil banana was used as the female parent. On the basis of space mutation, through continuous cultivation, screening and observation, two materials with obvious differences in biological and morphological characteristics were selected. In order to identify the genetic specificity of the two independently bred aerospace banana materials, the ISSR molecular marker technology was used in this study to screen out two primers with good polymorphism from 30 primers to analyze the two aerospace banana materials and 18 existing banana varieties. A total of 17 clear DNA bands were amplified by the two primers screened, of which 13 were polymorphic bands, accounting for 76.47% of the total bands, showing a high polymorphism at the DNA molecular level of banana materials. Electrophoresis showed that, combined with ISSR primers UBC881 and UBC847, the two aerospace banana materials had specific amplification bands, which could be distinguished from the other 18 banana varieties. Cluster analysis results showed that the genetic similarity coefficients between the 20 banana germplasm materials ranged from 0.545 to 1.000, with an average of 0.905; when the genetic similarity coefficient was 0.960, there were obvious genetic differences between the two bred aerospace banana materials, and the two bred aerospace banana materials with the female parent, and with other 17 banana germplasms. The results of this study would provide a strong basis for the breeding and identification of new varieties of aerospace bananas.

This study was conducted to explore the cumulative demand of nitrogen, phosphorus and potassium in disease-free sugarcane original seedlings, and provide reference for the nutrient management in the process of field propagation of disease-free sugarcane original seedlings. The growth of the disease-free sugarcane original seedlings of Zhongtang No. 1 in 2020 and 2021 was investigated, and the biomass and contents of nitrogen, phosphorus and potassium in roots, stems and leaves at various growth stages were determined for further analysis of the accumulation, phase absorption and daily absorption rate of nitrogen, phosphorus and potassium. It took 6 to 7 months for disease-free sugarcane original seedlings to reach 15 stem nodes from temporary planting of seedlings to the best harvest of seed canes. From July, August to late September (stem 1 to 2), the growth of sugarcane stems was the fastest. The cumulative increase of dry matter was the fastest in stem 4 (late October to late November), and this is the key stage of biomass accumulation. During the whole growth period of the disease-free sugarcane original seedlings, the content and accumulation of each element from high to low were potassium > nitrogen > phosphorus. Among the organs of roots, stems and leaves, leaves and stems always had higher nitrogen, phosphorus and potassium contents. The accumulation of nitrogen, phosphorus and potassium was mainly stored in the leaves before the stem elongation stage 1, and then mainly stored in the stems. The nutrient uptake rates of nitrogen, phosphorus and potassium at the seedling stage and tillering stage was 24.84%, 26.18% and 27.74%, respectively, and it was 55.54%, 58.61% and 52.30% at the stem 1 to 3 (late July to late October), while 19.62%, 15.20% and 19.96% during stem 4 and 5 (late October to late December). Reasonable fertilization can be carried out according to the phase absorption of each element, thereby improving the quality and economic benefits of disease-free sugarcane seedlings production. The demands of nitrogen, phosphorus and potassium in the breeding process of disease-free sugarcane original seedlings were clarified, which would provide a reference for the scientific and reasonable fertilization in large-scale field propagation of disease-free sugarcane original seedlings in the future, and improving the efficiency of the propagation and nutrient utilization of disease-free original seedlings.

Field experiments were conducted to study the relationship between nitrogen source, nitrogen application rate and the interaction on the source-sink development during the whole growth period of sweetpotato Mingmenjinshi and its relationship with yield and quality. The results showed that nitrogen application increased the chlorophyll content and net-photosynthetic rate of sweetpotato at 70 to 110 days after planting, the number of storage root per plant, average storage root weight and yield, the content of soluble sugar, sucrose, soluble protein, polyphenols and vitamin C, and significantly decreased the content of starch. Under the same nitrogen source, at 30 to 120 days after planting, the fresh weight of stems and leaves increased significantly with the increase of nitrogen application; the average number of storage root per plant, the average weight of storage root and the average weight of storage root per plant increased first and decreased then with nitrogen application, and were the highest when the nitrogen application rate was 120 kg/hm²; T/R first decreased and then increased with the increase of nitrogen application rate, and was the lowest when the nitrogen application rate was 120 kg/hm²; and the number of storage root per plant and yield was the highest with nitrogen application of 120 kg/hm². Under the high-yield nitrogen application rate of 120 kg/hm², compared with amide nitrogen and nitrate nitrogen, ammonium nitrogen significantly increased chlorophyll content and net-photosynthetic rate at 70 to 110 days after planting; significantly increased the fresh weight of leaves and stems at 30 days after planting; significantly increased the number of storage root per plant at 30 to 120 days after planting; significantly increased the weight of storage root per plant at 60 to 120 days after planting. At harvest, ammonium nitrogen significantly increased the yield of commercial storage root by significantly increasing the number of storage root per plant, also significantly increased the content of soluble sugar, sucrose, soluble protein and vitamin C, and improved flavor quality.

Considering that the serious shortage of available silicon content in typical paddy soil of Hainan Island, it is urgent to make reasonable application of silicon fertilizer. In this study, paddy soils developed from five typical parent materials (basalt, marine sediments, fluvial alluvium, sand shale, and granite) in Hainan Island were selected to investigate the effect of silicon fertilizer application on rice in a field plot experiment. Rice yield, quality and the related physiological, biochemical and agronomic indicators under different silicon fertilizer treatments were analyzed. Results showed that compared with the blank control, the silicon fertilizer application in both T₂ and T₃ treatments significantly increased the rice yield and its related indicators such as the number of stem tillers and effective heads, seed rates, 1000-grain weight, root activity, chlorophyll and crude cellulose content relative to the control. Rice quality such as milled rice, chalkiness and amylose content also reached a good level. It is generally recommended that the optimal amounts of Si fertilizer application are 750-950 kg/hm² (available SiO₂: 187-238 kg/hm²) for basalt-developed paddy soil and 625-935 kg/hm² (available SiO₂: 156-234 kg/hm²) for granite-developed paddy soil, respectively. Meanwhile, compared with the control, the amount of silicon fertilizer application in T₂ and T₃ treatments significantly increased the number of tillers, root activity, chlorophyll and crude cellulose content in paddy soil developed from marine sediments, river alluvial and sand shale. Rice yield reached the highest and rice quality reached a good level in T₂ treatment, but rice yield and its related agronomic indicators did not increase significantly with the increasing of silicon fertilizer application (T₃), and even some indicators exhibited a downward trend. It is recommended that the optimal amounts of Si fertilizer application are 560 kg/hm² (140 kg/hm² of available SiO₂) for paddy soil developed from marine sediments and river alluvial sediments, and 750 kg/hm² of silicon fertilizer (187 kg/hm² of available SiO₂) for paddy soil developed from sandy shale, respectively. Thus, this study revealed the effect of silicon fertilizer application in typical paddy soil of Hainan Island, providing a scientific basis for formulating the standard of silicon fertilizer application as well as demonstrating and popularizing high efficiency silicon application technology and of rice in Hainan province.

The study was aimed to screen out the excellent tobacco germplasm resources which could be used in the field of scientific research, production and breeding. Conventional chemical composition and major alkaloids were tested, compared and clustered for 141 flue-cured tobacco, 18 burly tobacco and 6 cigar germplasm resources from China and abroad. Total sugar and reducing sugar contents were high in flue-cured tobacco germplasms, while total nitrogen, nicotine and potassium oxide were high in burley tobacco germplasms. Total alkaloid and nicotine content were the highest in flue-cured tobacco germplasm Zilaihuang 2243, and the content of cigar germplasm Dutch (ohio) was the lowest. The nicotine and nicotine conversion rates were the highest in the tobacco germplasm Pingbanliu, and those for tobacco germplasm Erxingzi and Burley11B was the lowest. The 165 accessions were divided into 4 groups for clustering analysis. Flue-cured tobacco germplasms were mainly concentrated in Group 1 and 4, characterized by high total and reducing sugar content and low nicotinic conversion rate. Group 2 was low in total and reducing sugars, and high in total nitrogen, total alkaloids and potassium oxide. Group 3 had low nicotinoids and total alkaloids, high nicotinic reduction, and high nicotinic conversion rate. The chemical composition and alkaloids of different germplasm resources have significant difference. The selected germplasms with different gradients could provide useful material for further study of nicotine.

In order to clarify the salt tolerance range of Morinda citrifolia seedlings and the effect of salt stress on the growth of M. citrifolia seedlings, the M. citrifolia seedlings cultured in water for 180 days were used as materials, and the basic medium was 1/8 MS liquid medium, in which NaCl with mass fractions of 0, 0.2%, 0.4%, 0.6%, 0.8% and 1.0% were added respectively for stress treatment. The results showed that with the increase of NaCl stress concentration and stress time, the relative water content (RWC) and biomass of M. citrifolia leaves gradually decreased, and the contents of soluble protein (SP), malondialdehyde (MDA) and the activities of superoxide dismutase (SOD), catalase (CAT), ascorbic acid peroxidase (APX) and peroxidase (POD) gradually increased first and then decreased. The protective enzyme activity of M. citrifolia seedlings changes significantly with the increase of NaCl stress concentration and the passage of stress time. In the range of NaCl concentration below 0.8%, M. citrifolia can reduce damage and ensure growth by regulating osmotic substances and antioxidant enzymes. When NaCl concentration is in the range of 0.8% or above, the protective enzyme system and cell membrane are seriously damaged, which affects the growth of M. citrifolia. Therefore, the seedlings of M. citrifolia can be tested in the area with NaCl concentration below 0.8%.