Species and Occurrence Regularity of Diseases and Insect Pests Harming Baccaurea ramiflora Lour. in Guangxi

Zhiqiang YANG, Yanchun LU, Xianghua WANG, Ting JIANG, Dejin TAN, Dongying XU, Chong PENG, Wen HE*

1. Guangxi South Subtropical Agricultural Science Research Institute, Longzhou 532415, China; 2. Liuzhou Farmland Construction Guidance Station, Liuzhou 545005, China

Abstract [Objectives] The paper was to understand the species and harm of diseases and insect pests of Baccaurea ramiflora Lour. in Guangxi, and to provide basis for the prevention and control of diseases and insect pests. [Methods] From 2018 to 2021, a systematic investigation on diseases and insect pests of B. ramiflora was conducted in Dongxing City, Fangchenggang City, Longzhou County, Pingxiang City, Jingxi City and Napo County in Guangxi. [Results] There were 22 species of diseases and insect pests that harmed B. ramiflora in Guangxi, 7 of which were diseases and 15 were insect pests. Leaf blight (Fuasrium spp.) was the main disease at seedling stage, causing severe damage, and anthracnose (Colletotrichum gloeosporioides Penz.) caused moderate damage. Cyclosia papilionaris Drury and Chrysochus chinensis Baly had high frequency of occurrence, wide damage area and severe damage. Cyclosia panthono Stoll and Lcerya aegyptiaca Douglas caused moderate damage, while other insect pests caused light damage. [Conclusions] The study lays a foundation for the scientific prevention and control of B. ramiflora diseases and insect pests, and promotes the sustainable and rapid development of B. ramiflora industry in Guangxi.

Key words Baccaurea ramiflora Lour.; Diseases and insect pests; Species investigation

1 Introduction

BaccaurearamifloraLour. is a tropical and subtropical arbor fruit tree[1], distributed in India, Malaysia, Myanmar, Thailand, Vietnam, as well as Guangdong, Guangxi, Yunnan, Hainan and other regions in southwest China[2-4].

B.ramiflorawas originally a kind of wild fruit tree, which was introduced into the field or large-scale cultivation by farmers or enterprises because of rich nutrition and good taste. Luoetal.[2-3], Kongetal.[5], Zhangetal.[6], Xuetal.[7]have carried out researches on the resource distribution, breeding technology, fruit preservation and chemical composition analysis ofB.ramiflorafrom 2013 to 2020. But so far, there are few reports on the diseases and insect pests ofB.ramiflora. Guangxi is the main area of natural distribution and small-scale cultivation ofB.ramiflora, concentrated in Dongxing, Fangcheng, Longzhou, Pingxiang, Jingxi, Napo,etc.[2]. In recent years, with the increasing expansion ofB.ramifloraplanting area and the introduction of new varieties,B.ramifloradiseases and insect pests have increasingly aggravated. In the past, the study ofB.ramifloradiseases and insect pests was weak becauseB.ramiflorabasically grew in the wild, with relatively small artificial planting area, and less research institutions or researchers focusing onB.ramiflora. Therefore, the research team conducted a comprehensive investigation on the main diseases and insect pests in the development ofB.ramifloraindustry in Guangxi from 2018 to 2020, laying a foundation for scientific prevention and control ofB.ramifloradiseases and insect pests, and better promoting the sustainable and rapid development ofB.ramifloraindustry in Guangxi.

2 Materials and methods

2.1 Survey time and locationFrom 2018 to 2021, a general survey was conducted along the main distribution areas ofB.ramiflorain Dongxing City, Fangchenggang City, Longzhou County, Pingxiang City, Jingxi City and Napo County. Three fixed survey points were set up in Guangxi South Subtropical Agricultural Science Research Institute in Shangjiang Township, Zhubu Township and Binqiao Township of Longzhou County. In this study,B.ramifloraplants in nurseries, orchards, park roads and wild communities were investigated.

2.2 Survey content and methods

2.2.1Survey content. The species and occurrence ofB.ramifloradiseases and insect pests in Guangxi were comprehensively understood from the aspects of damage location, occurrence and damage degree through the combination method of field identification and indoor identification.

2.2.2Survey methods. According to the phenological period, planting distribution and the occurrence characteristics of diseases and insect pests ofB.ramiflora, the diseases and insect pests were investigated at seedling stage, flowering stage, fruiting stage, fruit expansion stage, fruit harvesting stage and shoot extraction stage by combining fixed point investigation and general census.

The disease incidence rate was investigated by diagonal five-point sampling method, and five trees were investigated at each point. Ten leaves were collected from each tree in the east, west, south and north directions, and the number of diseased leaves and the total number of leaves was investigated. Seedling diseases were investigated at fixed points in the nursery of Guangxi South Subtropical Agricultural Science Research Institute. The samples were collected by diagonal five-point sampling method, five seedlings each point, and the number of diseased leaves and the total number of seedling leaves were recorded.

The insect pests were investigated by diagonal five-point sampling method in orchards. One tree was selected at each point, and a fixed 1-2-year-old branch of lower, middle and upper crown in the east, west, south and north directions was investigated to carefully check the number of insect pests on the branches and leaves. Meantime, 5 panicles were selected according to this method, and the fruit damage was checked and recorded in detail.

2.2.3Identification methods of diseases and insect pests. The insect pests were preliminarily identified under anatomical microscope according to the morphological characteristics, and the species of the insect pest was further confirmed by referring toChinaInsectEcologyAtlas,InsectClassificationRetrievalTableandInsectTaxonomy[8-10].

The disease was preliminarily determined according to the pathogen type and post-onset characteristics. The disease samples were taken back to the laboratory for isolation and culture according toPlantDiseaseResearchMethods[11], and the species of the disease was further determined through morphological characteristics and DNA sequencing analysis.

2.2.4Calculation of damage degree of diseases and insect pests. The calculation and classification of damage degree referred to the classification expression method of Wangetal.[12]. The damage degree "+++" represented severe, and the damage area accounted for more than 50% of the whole leaf (fruit, stem,etc.) area; the damage degree "++" represented moderate, and the damage area accounted for 20%-50% of the whole leaf (fruit, stem,etc.) area; the damage degree "+" represented relatively light, and the damage area accounted for less than 20% of the whole leaf (fruit, stem,etc.) area.

3 Results and analysis

3.1 Survey results of diseases

3.1.1Species and damage of diseases. All kinds of disease samples collected during the investigation were numbered and brought back to Guangxi South Subtropical Agricultural Science Research Institute for indoor identification of pathogens. The results showed that there were 7 kinds ofB.ramifloradiseases in Guangxi (Table 1). Leaf blight (Fuasriumspp.) and anthracnose (ColletotrichumgloeosporioidesPenz.) occurred severely, and the incidence rates of the two diseases reached severe and moderate level, respectively. Sooty mold [Trispospermumacerinum(syd) speg.], fruit rot and moss ill occasionally occurred in wild plants lack of management, with relatively light damage.

Table 1 Species and damage degree of Baccaurea ramiflora diseases in Guangxi

3.1.2Damage characteristics of two diseases. (i) Leaf blight. Leaf blight was the main disease at the seedling stage, causing great harm to unlignified young seedlings. The incidence rate of seedlings was 40%-80%. When it severely occurred, the whole nursery was sick, causing seedling shortage of the nursery. At present, there are no related reports of this disease in China. The pathogen is preliminarily identified asFusariumspp. by isolation and identification, but the specific species and genus of this disease need further study. The pathogenic characteristics of leaf blight were as follows: the disease can infect during seed germination and cotyledon stage, which first started in cotyledon, and then expanded from cotyledon to terminal bud; the pathogen would infect from terminal bud down to root in severe cases, causing the death of the whole plant. After lignification of the seedling stem, the damage of the disease to the stem was weakened, and the main symptom was the dry spot on the leaf, which led to the dry off of leaves and the shrivelling of the top tip. The disease had a wide incidence during seedling cultivation, especially before the seedlings were lignified, and the mortality rate of seedlings was high. If there was no effective prevention and control measure, it probably caused the spread of the disease and caused serious losses to seedling cultivation.

(ii) Anthracnose. The investigation showed that the disease mainly occurred in leaves and pedicels, or there were occasionally disease spots on fruits. The seedlings with high air humidity and sufficient nitrogen fertilizer had a higher incidence of disease, and the leaves had typical whorl spots. The leaves fell off when the disease was serious. The pedicels became black, and the branches became dry in severe causes, leading to flower and fruit shedding.

3.2 Survey results of insect pests

3.2.1Species and damage of insect pests. The results of investigation and general survey showed that there were about 15 species ofB.ramiflorainsect pests in Guangxi, including 3 species of Hemiptera, 5 species of Lepidoptera, 2 species of Coleoptera, 2 species of Diptera, 2 species of Homoptera and 1 species of Orthoptera.CyclosiapapilionarisDrury, Chrysochus chinensis Baly andLceryaaegyptiacaDouglas were the three main insect pests with high damage rate (Table 2).

Table 2 Species and damage degree of Baccaurea ramiflora insect pests in Guangxi

3.2.2Damage characteristics of major insect pests. (i)CyclosiapapilionarisDrury.C.papilionarisDrury was found in Dongxing, Pingxiang, Longzhou,etc.The pest mainly damaged the young leaves and young shoots with larvae, resulting in incomplete leaves. In severe cases, there were only veins remained on branches, and the young shoots were bald, affecting the growth of the plant. It occurred from March to August every year, and was peaked from late March to early April and from mid-June to early July.

(ii)ChrysochuschinensisBaly. The adults were hidden in the daytime and came out at night, with large difficulties in control. The larvae lived in the soil and fed on the roots of plants, causing two damages of a single pest. The pest liked to gather together on young leaves and young shoots, bit leaves into holes and notches, or led to bald rods in severe cases, causing great impact on the growth ofB.ramiflora.

(iii)LceryaaegyptiacaDouglas. The newly hatched nymphs can crawl; the first instar nymphs gathered together for harm, and the second instar nymphs migrated to other leaves for harm. There were 10 pairs of waxy tentacle-like secretions around the second instar nymphs, and they could crawl freely on the large branches and trunk. The nymphs ofL.aegyptiacacongregated at new shoots and along the dorsal veins of leaves to suck the sap. Moreover, honey dew was excreted, which induced sooty mold. The leaves and branches withered and fell off in severe cases, leading to weak tree vigor or even death of the whole plant.

4 Conclusions and discussion

Through investigation, the species, distribution and damage ofB.ramifloradiseases and insect pests in Guangxi were basically understood. There were 4 fungal diseases, 1 moss ill and 2 physiological diseases. There were 15 species of insect pests belonging to Hemiptera, Lepidoptera, Coleoptera, Diptera, Homoptera, Orthoptera,etc.Leaf blight is the main disease ofB.ramifloraseedlings, which will cause great harm to seedling breeding.C.papilionaris,C.chinensisandL.aegyptiacaare the main insect pests ofB.ramiflora, which affect the growth ofB.ramiflora.

WildB.ramifloratrees mostly grow in cool wet environment such as canyons with streams, fengshui forests. Such environmental conditions easily induce leaf blight and harm the growth ofB.ramifloraseedlings. Leaf blight has high infectivity to unlignified seedlings and has become the most threatening disease in the breeding stage ofB.ramifloraseedlings. In order to cultivate healthy seedlings, the disease should be paid much attention in the process of seedling breeding, and effective comprehensive control measures should be taken.

With the development ofB.ramifloraindustry in Guangxi, factors such as planting area, planting varieties, cultivation environment and climatic conditions have changed, and the species and occurrence degree of diseases and insect pests change as well. At the same time, with the introduction of new varieties, scion,etc., new pests and diseases are also constantly emerging. Therefore, it is necessary to carry out long-term investigation, monitoring and forecast of diseases and insect pests in order to accurately grasp the occurrence dynamics of diseases and insect pests and control the threat of alien invasive species to the development ofB.ramifloraindustry. Therefore, the following three suggestions are put forward: pay attention to the inspection and quarantine work, avoid the introduction and spread of quarantine diseases and pests; strengthen the cultivation management mode to create environmental conditions that are not conducive to the occurrence of diseases and insect pests; strengthen investigation and research to grasp the occurrence dynamics and regularity of diseases and insect pests in time. Meantime, the training of disease and insect pest control technology for farmers should be strengthened to provide technical guidance for the prevention and control of diseases and insect pests. Timely prevention and control should be conducted according to the plant protection policy of "prevention first, comprehensive prevention", so as to avoid the epidemic of insect pests and diseases.