INVESTIGATION INTO DETERMINING THE RANGE OF POTENTIAL HOST PLANTS OF LUPIN ISOLATE OF COLLETOTRICHUM GLOEOSPORIOIDES PENZ

Małgorzata Jeske
Department of Phytopathology, University of Technology and Agriculture, Bydgoszcz, Poland

ABSTRACT

The study covered field and pot experiments which involved 16 papilionaceous plant species under provocative conditions with artificial inoculation. The infection was performed about six weeks after sowing, spraying plants with the suspension of Colletotrichum gloeosporioides conidia from white lupin. The observations of the occurrence of the disease and the spread of infection were made every seven days. Over the technical plant maturity, sampling 4 x 50 plants of each of the sixteen species investigated for further research, and then making microscopic preparations, the presence of the pathogen was confirmed. There was determined the size of conidia derived from the plants species tested which were infected with C. gloeosporioides. In the pot experiment, at the emergence stage the plants were sprayed with the suspension of conidia of the pathogen. Over full maturity, 10 plants of each species researched were sampled from each of the 4 pots and there was determined the percentage of plants infected with the pathogen. Another aim of the pot experiments was to verify whether the isolates of C. gloeosporioides isolated from infected species of the plants tested remained pathogenic towards lupin. Out of the 16 species of papilionaceous plants investigated, 13 species were infected with lupin isolate of C. gloeosporioides. These species can then maintain their inoculation potential of the pathogen. Black medick, white melilot and soybean did not show disease symptoms.

Key words: anthracnose, Colletotrichum gloeosporioides, diseases, lupin, hosts range.

INTRODUCTION

Colletotrichum gloeosporioides Penz, the cause of lupin anthracnose, is a polyphage of a wide range of occurrence, infecting numerous plant species, both crops and weeds, representing different families, as well as shrubs and trees. One of the diseases caused by this pathogen is tomato fruit anthracnose, being one of the main reasons of mass rotting of late-harvest fruits [13]. [11,12] report on C. gloeosporioides as the cause of anthracnose, posing a serious threat to about 80 shrub and tree species in Polish nurseries. Many authors describe C. gloeosporioides isolated from Stylosanthes genus, a papilionaceous plant grown in Africa and South America [3,7]. [5] isolated this pathogen from avocado and almond-tree, [14] from pear and apple tree, [10] from olive tree fruit, [8] from mulberry leaves and [9] from tobacco. Despite a big availability of reports on the occurrence of the pathogen on single host plant species, a report is missing which would offer a comprehensive discussion on the importance of these plants in the epidemic occurrence of anthracnose. It was then necessary to study the development conditions of C. gloeosporioides in more detail by determining the range of plants which could be the host of lupin isolates of C. gloeosporioides. Defining the range of these plants can appear to be extremely helpful when trying to control the agent of the disease and to avoid a potential neighborhood of susceptible plants. With that in mind, research was carried out to define a possibility of development of C. gloeosporioides on other coarse- and small-grained papilionaceous plants.

MATERIALS AND METHODS

The research conducted in 2000-2001 covered field and pot experiments in which sixteen papilionaceous plant species were tested under provoking conditions with artificial inoculation.

The field experiments were set up at Mochełek, at the Agricultural Experiment Station of the University of Technology and Agriculture in Bydgoszcz, on experimental microplots in the completely randomized design, as a single-factor experiment with four replications. In the second decade of April, on 16 microplots, each 4m² in size, the seeds were sown: white lupin – Lupinus albus L., sundial lupin – Lupinus polyphyllus L., faba bean – Vicia faba L. var. minor Harz, edible pea – Pisum sativum L. sensu lato, fodder pea – Pisum sativum L. sensu lato, vetch – Vicia sativa L. ssp. sativa, serradella – Ornithopus sativus Brot., red clover – Trifolium pratense L., crimson clover – Trifolium incarnatum L., white clover – Trifolium repens L., black medick – Medicago lupulina L., white melilot – Melilotus albus Medik., sainfoin – Onobrychis viciifolia Scop., soybean – Glycine max Merr., common bird’s foot trefoil – Lotus corniculatus L., common bean – Phaseolus vulgaris L.

Research was conducted with the use of C. gloeosporioides isolate B3/00 obtained from naturally infested white lupin cv. Bardo collected on experimental plot at the Agricultural Experiment Station in Mochełek. Isolate was grown on acidified (pH 5.5) PDA medium Difco. Petri dishes with such prepared isolate were stored at 25°C. After 10 days water suspension of conidia (3x10⁶·ml^-1) was prepared. The inoculation was performed about six weeks after sowing by spraying plants with the suspension of conidia of C. gloeosporioides, of the inoculum concentration in 1 ml of about 3 x 10⁶ spores. The treatment was provided in the evening. After inoculation the plants were covered with foil for twelve hours to ensure optimal conditions for infection. The observations of the disease symptoms and the spread of infection were made every seven days. Over the technical plant maturity, 4 x 50 plants from each microplot were taken, and in order to confirm the presence of the pathogen microscopic evaluation of places with visible diseases symptoms was conducted. There was determined the size of conidia from the plants species tested which were infected with C. gloeosporioides. For each species 4 microscopic preparations were made, measuring 100 spores in each.

The pot experiments were set up in the completely randomized block, in four replications, where a single replication was made up of 1 pot. At the emergence stage, similarly as in the field experiments, the plants tested were infected with a suspension of conidia of the pathogen. Over the period of full maturity, 10 plants of each species tested were sampled from each of the 4 pots and there was determined the percentage of plants infected with the pathogen. Another aim of the pot experiments was to verify whether the isolates of C. gloeosporioides obtained from the infected plant species tested remained pathogenic towards lupin. Prior to sowing into pots, ‘Bardo’ white lupin seeds were washed for 45 minutes in tap water, and then surface-disinfected in 1% HgCl₂ for 10 minutes and rinsed three times in sterile water. Over the lupin emergence stage, the inoculation was carried out with suspensions obtained from respective infected papilionaceous species plants, of the inoculum concentration in 1 ml of about 3 x 10⁶ conidia. There was defined the percentage of plants infected with the pathogen. The pot experiments were made in two series. The results presented in the experiments are an arithmetic mean for the two series.

Obtained results were statistically analyzed with variation analysis and Tuckey’s test. Per cent of infected plants was transformed into Bliss’ angular degrees.

RESULTS AND DISCUSSION

Most of the papilionaceous plant species tested showed to be more or less considerably susceptible to infection with lupin isolate of C. gloeosporioides (Fig. 1). The percentage of the infected plants of the species researched ranged from 17 to 83%. In the first research year the lowest number of plants was recorded on red clover – 17% and common bean – 18%, while in the successive year – crimson clover and bean (20% each). A slightly higher infection in the first year was found in crimson clover, sainfoin (26% each) and common bird’s foot trefoil (29%), and in the second year – red clover (23%), common sainfoin (26%) and white clover (28%). A higher infection (from 32 to 49%) was reported in the first year for white clover, vetch, edible and fodder pea, serradella and faba bean, and in the successive year (from 31 to 44%) common bird’s foot trefoil, fodder pea, faba bean, vetch, edible pea as well as serradella. The species which was most infected of all in both years were: white and sundial lupin. The infection was not found in three of the sixteen species tested: black medick, white melilot and soybean. As a result of comprehensive research carried out in the United States, the plant species of different genera which could serve as plant hosts of C. gloeosporioides were examined. Out of 43 genera researched, representing different botanical families, the papilionaceous ones were the only ones which were susceptible to that pathogen [2,15]. Lupin isolate of C. gloeosporioides, in the present research, less or more considerably infected most of the papilionaceous plants tested. Although the infection of the species researched, except for faba bean, did not result in such typical external symptoms as it did in lupin, however, from the point of view of epidemiology, the very fact of infecting them seems to be very important. The species can maintain the pathogen inoculation reservoir and contribute to the spread of the disease. With that in mind, starting lupin plantations, one should pay attention to the fact what plant species are grown in the neighborhood of our field. In this way it would be possible to avoid an additional source of infection.

Considering two research years, it was observed that the spores widths and lengths ranged from 4 to 8ľm x 6-16µm. Many authors [1,4,6] confirm ranges of width and length of conidia obtained in these studies.

Very similar results were reported in the pot experiment. Similarly as in the field experiment, symptoms of infection with the pathogen were observed in thirteen out of the sixteen papilionaceous plant species researched (Fig. 2). The infection was in all cases lower than under field conditions. Similarly as in the field conditions, it was white lupin which showed to be most infected (70%), followed by sundial lupin (50%). The lowest number of infected plants was found in common bean (13%). The infection of the other species, although slightly differentiated, remained similar to those described above.

The research results of the possible white lupin plants infection with isolates of C. gloeosporioides, isolated from infected papilionaceous plants in field conditions are given in Fig 3. All the isolates separated were found to be pathogenic towards lupin showing characteristic symptoms of the disease. The percentage of the infected plants ranged from 2.5 to 20. The lowest number of diseased plants was found in lupin infected with the isolate obtained from common bean, while the highest – with the isolate separated from white lupin. The infection of the other plants remained at a similar level, only when infected with the isolate obtained from sundial lupin remained slightly higher (17%).

It was also found that in 2001 (Fig.3) percentage of infected plants in pot experiment was three times lower in all combinations as compared with 2000 (Fig.2), probably due to reduced pathogenicity of researched isolates after one year storage on slant agars. [16] report that three months of seed storage resulted in lower viability of C. gloeosporioides dependently on temperature from 5 to 80%.

CONCLUSIONS

1. Out of the sixteen papilionaceous plant species tested, thirteen of them were infected with lupin isolate of C. gloeosporioides. No characteristic external symptoms, similar as in lupin (except for faba bean), can suggest their greater tolerance towards this fungus.

2. Reisolating C. gloeosporioides from papilionaceous plants confirmed its pathogenicity towards lupin.

REFERENCES

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Accepted for print: 18.08.2006

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