Root rot of lavender caused by Phytophthora nicotianae

Lavender (Lavandula angustifolia) plants with rotted roots and discoloured vascular systems consistently yielded cultures of fungi that were identified as Phytophthora nicotianae van Breda de Haan (= P. parasitica). Inoculation experiments using either zoospore suspensions or mycelial fragments were successful in reproducing symptoms originally observed on wilting and dying plants. Lavender is a new host for P. nicotianae.     

Root rot of tree lucerne caused by Phytophthora nicotianae

Phytophthora nicotianae Breda de Haan was consistently isolated from rotted roots and discoloured vascular tissues of tree lucerne ( Chamaecytisus palmensis ). It was identified with the aid of total DNA restriction fragment length polymorphisms and morphological characters. Pathogenicity was demonstrated by inoculation. This is the first record of P. nicotianae on tree lucerne in South Africa.     

Phytophthora rot of alpine delphinium caused by Phytophthora sp. kelmania

Severe stunting and root rot were observed on alpine delphinium plants (Delphinium elatum) from Aomori Prefecture, Japan, in 2010 and 2011. A Phytophthora isolate from the diseased crown was identified as Phytophthora sp. kelmania based on morphological characteristics and DNA sequence data. Inoculation of alpine delphinium plants with the isolate produced a similar root rot. Pathogenicity of the isolate on four species of plants that are known hosts for P. sp. kelmania was confirmed. We propose the name “Phytophthora rot” (eki-byo in Japanese) for the present new disease on alpine delphinium.

     

Storage rot of swede caused by Phytophthora sp.

During long-term storage trials of swedes ( Brassica napus ) carried out during five seasons between 1982 and 1987, storage rots caused by a Phytophthora sp. were observed, the first report of the disease in the UK.     

非洲菊疫霉根腐病的快速分子诊断

 隐地疫霉引起的根腐病是非洲菊生产上的主要病害,为发展该病的快速诊断技术,本文比较了卵菌核糖体基因ITS的序列,在此基础上设计了2条针对隐地疫霉的特异性PCR引物PC1和PC2。供试的23种不同真菌和疫霉菌的46个菌株中,利用这对引物能从隐地疫霉基因组DNA中扩增出一条分子量为620bp的特异性条带,该引物的检测灵敏度可达10pg。采用快速组织碱裂解法提取发病植物组织的DNA,结合PCR检测技术,4h内可从发病的非洲菊根部组织中特异性地检测到隐地疫霉菌。结果表明,建立的非洲菊疫霉根腐病菌分子检测方法可用于该病害的快速分子诊断。     

Crown rot caused by Phytophthora cactorum in Norwegian strawberry production

Crown rot of strawberry, caused by Phytophthora cactorum , was detected for the first time in Norway in 1992. This paper reports on surveys for P. cactorum in Norwegian certified strawberry plant production and on the distribution of the pathogen in regular strawberry production. In 1996 and 1997, samples of plant material from all certified strawberry plant growers in the country were investigated by isolation on artificial growth medium and using an enzyme-linked immunosorbent assay (ELISA). P. cactorum was not detected in any of the samples. A total of 171 isolations from plants with symptoms resembling crown rot were made from plants in a survey of the distribution of Phytophthora fragariae var. fragariae and from other samples. P. cactorum was detected at 35 different strawberry-producing farms in 11 of the 19 counties of Norway. The fungus was most frequently isolated from cv. Korona (at 18 locations), followed by cv. Inga (at 10 locations).     

Root rot of hyacinths caused by species of Pythium

The root rot widely seen in hyacinth was found to be caused byPythium spp. instead of byFusarium culmorum. Of sixPythium species isolated, three, includedP. ultimum andP. violae, were investigated in glasshouse experiments and their pathogenicity demonstrated. In these experiments plants were successfully grown in containers in which an aqueous mist was maintained, or in water cultures. In experimental plots on infected soil, Dexon, a fungicide selective for Pythiaceae, distinctly reduced the number of dead plants and increased yield and bulb size, thus confirming the role ofPythium in causing root rot. Practical application of Dexon deserves further attention.     

Effects of fungicides on apple crown rot caused by Phytophthora cactorum

The mycelial growth of Phytophthora cactorum on corn meal agar was completely inhibited by metalaxyl or mancozeb at 50 or 100 μg ml^?1, but not by fosetyl-aluminium at the same concentrations. Soil drenches with metalaxyl, followed by metalaxyl+mancozeb, around the base of naturally infected trees under orchard conditions, prevented the growth of P. cactorum in the infected bark of the tree. Soil drenchs with metalaxyl, followed by metalaxyl+mancozeb, also prevented the infection of apple trees with P. cactorum under orchard conditions. The trunk circumference and spur length were not significantly affected by any of the fungicide treatments in all the trials over 2 years, except in one of the four orchards used in the study. Soil drench with metalaxyl alone, or followed by metalaxyl+mancozeb, may provide an effective control method for crown rot of apple trees.     

Root rot inCampanula carpatica caused byPhytophthora cryptogea

This is the first record of root rot inCampanula carpatica as well as in the genus ofCampanula caused byPhytophthora cryptogea. An attack was observed in potted plants grown in a greenhouse on ebb- and flow benches and with recirculation of the nutrient solution. The fungus caused wilting of the leaves together with discoloration and rotting of the roots. Pathogenicity tests showed that the isolate ofP. cryptogea fromC. carpatica attactedGerbera jamesonii and vice versa. Treatment with the fungicide furalaxyl was able to reduce disease development.     

Development stage-dependent susceptibility of cocoa fruit to pod rot caused by Phytophthora megakarya

Pod rot causes up to 30 % losses in world cocoa production. In order to predict the risk evolution of disease, it is important to take into consideration the developmental stage of fruits. In fact, it has been shown that the risk of attack by pod rot depends amongst others on the developmental stage of fruits. We proposed here to estimate the susceptibility at different stages. Susceptibility of fruit to disease was investigated at three fruit developmental stages (cherelle, young pod and adult pod); disease severity was assessed in laboratory conditions, on detached, artificially inoculated fruits, while disease incidence was assessed in the field, under natural inoculum pressure. In both assessment fruits at the cherelle stage were the most susceptible whereas the young and adult fruits were equally susceptible. The vertical position of the fruits on the tree did not influence their susceptibility. Estimates of the fruit susceptibility and of the infectious potential were derived from the severity and incidence measurements, using a model assuming that the number of spores on a fruit follows a Poisson distribution with the mean, the density of spores per fruit as the parameter. The estimated parameter values allowed the evaluation of the probability of attack of a fruit by the disease, which could be implemented in a disease warning system.     

Soybean root suberin and partial resistance to root rot caused by Phytophthora sojae

Phytophthora sojae is the causal agent of root and stem rot of soybean (Glycine max). Various cultivars with partial resistance to the pathogen have been developed to mitigate this damage. Herein, two contrasting genotypes, the cultivar Conrad (with strong partial resistance) and the line OX760-6 (with weak partial resistance), were compared regarding their amounts of preformed and induced suberin components, and to early events during the P. sojae infection process. To colonize the root, hyphae grew through the suberized middle lamellae between epidermal cells. This took 2 to 3 h longer in Conrad than in OX760-6, giving Conrad plants more time to establish their chemical defenses. Subsequent growth of hyphae through the endodermis was also delayed in Conrad. This cultivar had more preformed aliphatic suberin than the line OX760-6 and was induced to form more aliphatic suberin several days prior to that of OX760-6. However, the induced suberin was formed subsequent to the initial infection process. Eventually, the amount of induced suberin (measured 8 days postinoculation) was the same in both genotypes. Preformed root epidermal suberin provides a target for selection and development of new soybean cultivars with higher levels of expression of partial resistance to P. sojae.     

Evaluation of Trichoderma harzianum for controlling root rot caused by Phytophthora capsici in pepper plants

The ability of Trichoderma harzianum to control the rotting of pepper ( Capsicum annuum ) plant roots caused by Phytophthora capsici was studied. Interactions between the fungi were assessed in vitro on three culture media (V8c, Czapek and 2% water agar) and in vivo in plants grown in a substrate inoculated with P. capsici and T. harzianum . Studies on mutual antagonism in vitro showed that P. capsici was inhibited by T. harzianum ; however, the intensity of inhibition differed according to the medium used, being greatest on Czapek. Analysis of the fungal populations in the plant growth substrate showed that T. harzianum consistently reduced that of P. capsici over time. This reduction in the pathogen population was associated with a reduction in root rot of between 24 and 76%, although plant growth (dry weight) was still reduced by 21.2–24.7%, compared with the uninoculated control. In the absence of T. harzianum with the same pathogen inoculum levels, the reduction in dry weight was 59.8–68.6%, suggesting that T. harzianum reduced the damage.     

The occurrence of crown rot caused by Phytophthora cactorum in the apple rootstock MM 104

Samenvatting In het voorjaar van 1968 vertoonde een aantal bomen op het onderstammen proefveld te Kraggenburg (N.O.P.) een slechte bladstand. Vóór januari 1969 waren alle bomen van de appelrassen Cox's Orange Pippin, James Grieve en Lombartscalville en één enkel geplante Stark Earliest, alle geënt op onderstam MM 104, afgestorven. Slechts de vijf bomen van het ras Golden Dilicious op MM 104 vertoonden een normale stand. Uit de aangetaste wortels konPhytophthora cactorum geïsoleerd worden. Vermoedelijk heeft het pathogeen door een hoge grondwaterstand gedurende de winter 1967/1968 de kans gekregen de onderstam MM 104 te infecteren. Doordat de vijf Golden Delicious bomen op MM 104 aan het windscherm grensden, waar het relatief droger is, zijn deze waarschijnlijk aan infectie ontsnapt.     

Leaf and head rot of Chinese cabbage - a new field diesease caused by Pythium tracheiphilum Matta

A new disease has arisen in field grown Chinese cabbage (Brassica campestris ssp. pekinensis) in Denmark. The soil-borne causal agent was shown to be Pythium tracheiphilum Matta, a little known pathogen of lettuce. Until now, outbreaks of the disease in Chinese cabbage were generally attributed to Phytophthora porri Foister, since symptoms of the disease in the field resemble those caused by Ph. porri in Chinese cabbage in cold stores. In some severely affected crops harvest losses in 1994, directly attributable to P. tracheiphilum, were estimated to about 50%, corresponding to a market value of up to $ US 20000 per ha. Outbreaks of the disease coincide with the heading of the crop, while juvenile plants or seedlings are apparently not attacked. It appears that the outer leaves are infected directly from the soil. Mainly above ground parts are affected and colonized by the pathogen, and indications of infection via the root system have not been observed. This is the first record of P. tracheiphilum as a pathogen of Chinese cabbage.     

Pythium rot of Chinese cabbage (Brassica rapa L. subsp. pekinensis) caused by Pythium aphanidermatum

Severe rot was found at the base of leaves and stems of Chinese cabbage (Brassica rapa L. subsp. pekinensis) in Ibaraki Prefecture every year in early September from 2002 through 2004. The causal fungus was identified as Pythium aphanidermatum (Edson) Fitzpatrick. This is the first report of P. aphanidermatum on Chinese cabbage. A similar disease of Chinese cabbage caused by P. ultimum Trow var. ultimum is known as Pythium rot. We propose adding P. aphanidermatum as a new pathogen of this disease.