Horizontal transmission and host-virulence attenuation of totivirus in violet root rot fungus Helicobasidium mompa

Monokaryotic strains of Helicobasidium mompa were used as vectors of a mycovirus between various H. mompa isolates to examine the transmissibility of one of the mycoviruses, totivirus (HmTV1–17 virus) in the hypovirulent isolate V17 of H. mompa. The isolates that acquired HmTV1–17 virus were also examined for any alteration in the virulence. Twelve dikaryotic isolates of H. mompa, belonging to 11 mycelial compatibility groups (MCGs) and being mycelially incompatible with isolate V17, were used as recipients of HmTV1–17 virus. Two monokaryotic isolates that were mycelially incompatible with isolate V17 and all of the recipients were also used as vectors of HmTV1-17 virus between isolate V17 and the recipients. When isolate V17 and recipients were directly paired on plate media, HmTV1-17 virus was transmitted from isolate V17 into 2 of the 12 recipients (i.e., 2 of the 11 MCGs). Two monokaryotic strains were paired with isolate V17, and the monokaryotic strains that acquired HmTV1-17 virus were then used as new virus donors. When the monokaryotic strains containing HmTV1-17 virus were paired with the 12 recipients, HmTV1-17 virus was transmitted into 7 of the 12 recipients from the monokaryotic strains (i.e., 7 of 11 MCGs). Based on these results, we concluded that monokaryotic strains could act as vectors to transmit HmTV1-17 virus into H. mompa isolates. When four of the H. mompa isolates that acquired HmTV1-17 virus were used to inoculate apple rootstock Malus prunifolia, the virulence of all of the isolates was attenuated from that of their parental isolates. Moreover, because the DNA fingerprints of the fungal isolates that acquired HmTV1-17 virus were the same as those of their parental isolates, the infection with HmTV1-17 virus is considered the cause of virulence attenuation of H. mompa.     

An Improved Method for Isolating Violet Root Rot Fungus, Helicobasidium mompa, from Basidiocarps

Basidiocarps of the violet root rot fungus, Helicobasidium mompa, are less frequently used for isolation than are mycelial strands and sclerotia even though the basidiocarps are conspicuously produced at the trunk base of diseased plants. Basidiocarps are also more suitable for storage. This paper describes an improved method for obtaining pure cultures from basidiocarps using microcentrifuge tubes to facilitate the awkward steps of rinsing fungal materials under a dissecting microscope. Received 28 June 2000/ Accepted in revised form 4 August 2000     

牡丹紫纹羽病病原菌的生物学特性及其防治

紫纹羽病是引起牡丹病害的主要病原真菌之一。采用定点、定时、定株观察与田间普查相结合,结合致病菌的室内分离培养和药剂毒力筛选测试、田间小区防治试验,研究了牡丹紫纹羽病病原菌的生物学特性及其防治措施。结果表明,病害严重发病时期为3月下旬至5月中下旬,病原菌生长最适pH为5.8左右,最适生长温度为25￣26℃;药剂毒力筛选测试效果70%甲基托布津的抑菌率为93.7%;45%代森铵水剂抑菌率为91.4%。以70%甲基托布津1000倍液或45%代森铵1000倍液每窝1000ml进行灌窝,能达到较好的防治效果。     

杨树紫纹羽病发生与防治

近几年杨树紫纹羽病在苏鲁两省发生严重，受害杨树品种主要为中菏1号杨、中菏2号杨、I-107杨、I-69杨、I-72杨和中林46杨，其林木的发病率高达80％以上。经定点研究已知该病由卷担子菌Helicobasidium brebissonii（Dosm．）Donk]引起，并已了解该病的发病症状及发病规律。其药剂防治试验结果表明，用WP100倍的4JD％福美砷、14．5％多效灵和70％甲基托布津药液灌根后作晾土处理的防治效果均在70％以上。其病情指数从防治前的25—30下降到防治后的11．7—15．0。其中以用40％福美砷药液灌根后晾土处理的防治效果最好。     

Hypovirulent strain of the violet root rot fungus <Emphasis Type="Italic">Helicobasidium mompa</Emphasis>

The hyphal tip was isolated from 13 weakly or moderately virulent strains of Helicobasidium mompa to remove double-stranded (ds) RNAs and demonstrate their role as the hypovirulence factor. All of 829 hyphal tip subcultures retained dsRNAs. However, strain v670 containing two large fragments (10kb) and one small fragment (ca. 2.3kb) of dsRNA lost the largest fragment in 3 of 63 subcultures analyzed. One of the three subcultures (v670hti) was used to inoculate carrots to regain virulence compared to the parental strain v670. When isolate v670hti was paired with v670, the largest fragment was reintroduced to v670hti, and its virulence was diminished. Northern blot analysis with two probes hybridizing dsRNA fragments in most H. mompa strains revealed that the largest fragment involved in hypovirulence was different from two other fragments that are common in Japan. These results indicate that the largest dsRNA fragment in strain v670 is associated with hypovirulence in H. mompa.     

<Emphasis Type="Italic">Helicobasidium mompa</Emphasis> isolates from sweet potato in continuous monoculture fields

 Isolates of the violet root rot fungus Helicobasidium mompa were collected from herbaceous and tree plants. Their host preference was studied by inoculation experiments using carrots, sweet potatoes, and apple stocks. It was found that sweet potato isolates from Kyushu produced infection cushions on carrots and sweet potatoes but not on apple stocks. Other isolates did not show host preference. Sweet potato isolates were also characterized by ready hyphal mass (sclerotium) production. They were thought to have adapted to the habitat with high disturbance by annual tillage. Received: July 15, 2002 / Accepted: September 26, 2002     

牡丹紫纹羽病病原菌的生物学特性及其防治

紫纹羽病是引起牡丹病害的主要病原真菌之一。采用定点、定时、定株观察与田间普查相结合,结合致病菌的室内分离培养和药剂毒力筛选测试、田间小区防治试验,研究了牡丹紫纹羽病病原菌的生物学特性及其防治措施。结果表明,病害严重发病时期为3月下旬至5月中下旬,病原菌生长最适pH为5.8左右,最适生长温度为25~26℃;药剂毒力筛选测试效果70%甲基托布津的抑菌率为93.7%;45%代森铵水剂抑菌率为91.4%。以70%甲基托布津1000倍液或45%代森铵1000倍液每窝1000ml进行灌窝,能达到较好的防治效果。     

桑树紫纹羽病菌侵染桑根的生长动态观察

通过对桑园土壤垂直剖面调查,桑紫纹羽病菌80%以上集中在10~30cm的土层,50cm以下土层没有发现病根。利用两面玻璃根箱内的带菌土壤栽植桑苗,观察到了紫纹羽病菌丝在土壤中缓慢生长,但接触健康根系后一般不会感染,而菌索大多能感染健康桑根,当病原菌和桑根建立寄生关系后,菌丝在桑根表面迅速蔓延。人工培养基栽种桑苗后接种病原菌,茎叶切除的桑苗比不切除的桑苗感染速度更快。     

硬枝杆插法用于桑树紫纹羽病的诊断和药剂防效鉴定的研究

采用硬枝扦插调查了桑紫纹羽病的发病过程、症状的发展、发病率、地上部外观表现、根部病症等 ,认为该方法诊断桑树紫纹羽病具有快速、简便、准确的特点 ,适用于药剂防治效果鉴定。选择 7种杀菌剂进行防治效果试验 ,调查根部菌丝着生情况 ,以五氯硝基苯的防治效果最好 ,平均防效达 81 4 % ,硫酸铜最差 ,平均防效为 34 2 % ,且 7种药物的防治效果都是灌根处理优于撒土处理。     

A Root Box Method to Estimate Virulence of Helicobasidium mompa Using Carrots and Its Comparison with the Conventional Method Using Apple Stocks

A root box method with carrots was developed to estimate virulence of the violet root rot fungus, Helicobasidium mompa, to facilitate short-term screening of many isolates during a year. The root box consisted of two transparent acrylic plates and a plastic bag of vermiculite in which two taproots of carrot were growing and inoculated with the fungus growing on fragments of mulberry twigs. The boxes were kept in a greenhouse at 25°C, and the surface of carrots was observed weekly up to 14 weeks. The virulence of each isolate was determined based on the number of weeks after inoculation required for the fungus to develop infection cushions on the surface of carrots. Results were compared with those from the conventional inoculation method using apple stocks. Two-year-old 456 apple stocks were planted with or without fungal inoculum in 30-cm diam. plastic pots containing commercial soil and placed outdoors in April 1999. Symptoms on plant tops were observed weekly, and the first stocks were killed 14 weeks after inoculation. At the end of trial 1 (6 months) and trial 2 (14 months), apple stocks were dug up to rate disease index (DI) based on hyphal growth and infection cushion formation on the stem base. There was variability in disease severity among replicates as well as isolate variability ; however, the results were similar in both trails. The level of virulence estimated by both methods was almost parallel for a total of 23 isolates from five plant species, except for two isolates from sweet potato that formed no obvious infection cushion on apple roots but on carrot were the most virulent. Received 11 December 2000/ Accepted in revised form 23 March 2001