Lin, C. P.1, *, Tsai, J. N.1, Ann, P. J.1, Chen, P. R.1, Chang, J. T.1 and Hsu, T. H.1
1 Plant Pathology Division, Taiwan Agricultural Research Institute, COA
* Corresponding Author，E-mail: [email protected]; FAX: +886-4-23302803
Abstract
Pitaya (Hylocereus spp.) is one of the important newly emerging fruit crops in Taiwan. Fruit wet rot, a severe postharvest disease of pitaya caused by Gilbertella persicaria var. pitaya, was first found in August 2009. Fruit infection occurred in the field during rainy season with a small water-soaked lesion around the stem-end, which developed into fruit soft rot within 3-5 days after harvest. Occasionally, fruit soft rot initiated from lesions on fruit skin or scales, and internal black rot of fruit were also observed. Results of survey of pitaya orchards showed that infection of G.
persicaria var. pitaya on young fruits or on flower buds and petals resulted in the development of symptoms similar to that observed in the postharvest fruits. Most of the infected fruits in the orchard failed to develop normally and dropped prematurely.
However, in regards of the differences of the number of splitted sporangial wall, ITS sequence and virulence to fruits of pitaya, the G. persicaria var. pitaya was different from the holotype of G. persicaria. Brown to black sporangia of G. persicaria var.
pitaya were formed on the surface of infected tissues, especially under humid conditions. Our data showed that tissue wounding was an important factor affecting the disease severity. G. persicaira var. pitaya were pathogenic on unwounded fruits of peach and guava, and wounded fruits of apple, mango, persimmon, plum, wax apple and tomato, but they were non-pathogenic on starfruit, melon, banana and kiwifruits.
The results of chemical selection showed that cyprodinil + fludinoxonil, pyraclostrobin, prochloraz-Mn, tridemorph, difenoconazole and tebuconazole, fluazinam were the potential fungicides for controlling the disease. As for organic farming, the data showed that Bordeaux mixture and both cinnamon oil products, - Hey-Show-Lo and Tan-Wu-Zung- could inhibit mycelial growth and sporangiospores germination well. To control the disease, apply mycelial-growth- inhibiting chemicals the before raining to protect the fallowers and young fruits from infection and sporangiospores-germination- inhibiting chemicals after raining to treat the infected tissues. The infected tissues should be excised out of the orchards immediately therefore avoiding further infection of the fruiting fruits or other tissues. Also, harvest in the raining day should be avoided to reduce the infection rate during storage.
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Table 1. Morphological characteristics of Gilbertella persicaria var. persicaria and G.
persicaria var. pitaya.
Characters Gilbertella persicaria
var. persicaria Gilbertella persicaria var. pitaya
Sporangiophore
(branched or rarely branched; bent when young, upright at maturity)
19-33 μm in diam 18-50 μm in diam
Sporangia
(yellow to dark brown, more or less globose; covered whith calcium oxalate crystals)
45-170 μm in diam. 60-115 μm in diam
Columella
(with basal collar; obpyriform, obovoid to cylindrical)
36-81 μm in diam. at
the widest 25-60 μm in diam. at the widest
No. of longitudinal suture
(on the surface of sporangia wall) 1 1-5
No. of separated sporangial wall 2 2-7 (avg. 4) Sporanigospores
(globose, ellipsoid to ovoid) 5.1-17.8 × 3.8-12.7 μm 5.5-11.8 × 4.5-8.8 μm No. of hyaline appendages
(up to 24 μm, at the ends of sporanigospores)
2-7 0-3
Chlamydospores
(globose to irregular; light brown, smooth-walled)
15-29 × 10-16 μm 18.9-25.4 × 14.9-23.8 μm
Table 2. Differences of diagnostic characters between Rhizopus stolonifer and Gilbertalla persicaria var. pitaya.
Characters Rhizopus stolonifer Gilbertalla persicaria Sporangiospore
with appendages No Yes Max. growth temp. 33 oC 38 oC
Rhizoid Yes No
Sporangiophores Branchless; erect Branched or rarely branched; bent or upright
Sporangia diam. Up to 200-300 μm Less than 180 μm.
Sporangial wall No Yes
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Table 3. Effect of wounded treatment on infection rates of pitaya fruit caused by Gilbertalla persicaria var. pitaya 1.
1: The harvested fruits (Hylocereus undatus) were inoculated with cottons which were pre-immersed in spores suspensions for 1-3 min; wound were made by bug needles;
spores suspensions concentration = 2× 106 spores/ml. This experiment were repeated for 2 times
2: dpi stands for “day post infection”.
Table 4. Test of fruit host ranges of Gibertela persicaria var. pitaya in Taiwan 1 Name of tested fruit
Infection rates(%)2
Unwounded Wounded
Peach (Prunus persica) 100 100
Guava (Psidium guajava) 16.7 33.3
Pear (Pyrus pyrifolia) 0 100
Plum (Prunus salicina) 0 100
Persimmon (Diospyros kaki) 0 100
Tomato (Solanum lycopersicum) 0 100
Mango (Mangifera indica) 0 91.7
Apple (Malus domestica) 0 87.5
Wax apple (Syzygium samarangense) 0 50
Banana (Musa sapientum) 0 0
Kiwifruit (Actinidia deliciosa) 0 0
Melon (Cucumis melo) 0 0
Starfruit (Averrhoa carambola) 0 0
1. Fruits were inoculated with cottons which were pre-immersed in spores suspensions of G. persicaria var. pitaya isolate F210187 for 1-3 min and infection was counted 72 hr post infection; wounds were made by bug needles; spores suspensions
concentration = 2× 106 spores/ml. This experiment was repeated for 1-2 times.
2: The inoculation sites were counted as infected only if soft-rot symptoms appeared within 7 day post inoculation and G. persicaria var. pitaya can be reisolated again.
Isolate dpi2
Infection rates (%) Unwounded Wounded
F212122 1 0 100
2 77.7 (±29.8) 100
F210187 1 0 100
2 0 100
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Fig. 1. Gilbertella persicaria caused wet rot symptoms on flower bud (A), petals (B), young fruit (C, D) and harvested fruit of pitaya (E).
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Fig. 2. Morphology of asexual reproduction structures of Gibertella persicaria var.
pitaya produced on fruit tissues (A - B) and PDA (C - F). A: mature sporangia produced on curved (mostly) sporangiophores. B: persistent sporangial wall with longitudinal sutures. C: sporangial wall could separate into 2 - 5 pieces (in the case of this picture were 4 pieces). D: sporangial wall covered with crystalline spines. E: a columella with collar (arrow). F: a spore with two hyaline appendages (arrows), stained by rose bengal. G:. an intercalary chlamydospore produced by G. persicaria var. pitaya on MEA. Bar = 10 μm.
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Fig. 3. Effect of temperature on mycelial growth of Gibertella persicaria var. pitaya isolates. Cultures were grown on PDA in petri dishes (diam. 9 cm) for 2 days. Linear growth rates were shown as average of 3 replicates of each isolates in a single experiment. This experiment was repeated for 3 times with similar results.
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