Seeds as Vehicles for Pathogen Importation

Since the 1900s, consumer demand for new plant products gave opportunity for many plant pathogens to disseminate to new areas on imported seeds. New markets for plant commodities encouraged plant breeders to begin collecting seed stocks from abroad. The birth of new seed companies extend their markets to new area. These events began the global dissemination of many seedborne pathogens. Many seedborne pathogens gained entry and escaped detection by specific traits that favored their dissemination. Three recent case scenarios are presented that illustrate how plant pathogens that passively employ the seed coats of their host achieved global dissemination and permanence in each patho-system. Evidence is presented to show that asparagus (Asparagus officinalis) seed produced in the US acted as a vehicle for disseminating one vegetatively compatible group (VCG) of a pathogenic fungus on asparagus called Fusarium proliferatum throughout new plantings in Australia. Similarly, public demand for Mediterranean cuisine in the US and abroad during the last 20 years led to an increase in the importation of basil (Ocimum basilicum) seed along with an inconspicuous fungus called Fusarium oxysporum. The fungus caused a destructive disease called Fusarium wilt of basil that appeared in over 25 separate locals spanning three continents. The third example demonstrated how new developments in lupine (Lupinus spp.) cultivars and increased public demand led to the global dispersal of a seedborne pathogen called Colletotrichum gloeosporioides. Each case highlights how these pathogens use seeds, humans, and particular traits to disperse globally in short period of time.     

Inhibition of photosynthesis by Colletotrichum lindemuthianum in bean leaves determined by chlorophyll fluorescence imaging

Infection of bean leaves by Colletotrichum lundemuthianum causes vein necrosis and subsequent localized wilting of the blade. The effect of infection on photosynthesis was investigated by imaging leaf chlorophyll fluorescence as a means of mapping stomatal and metabolic inhibition of photosynthesis. During infection, CO₂ assimilation (An), stomatal conductance to water vapour, and photosynthetic electron transport rate (J_t) decreased, whereas dark respiration increased. An decreased more than was expected from the reduction in green leaf area, showing that photosynthesis was inhibited in apparently healthy areas. Under subsaturating irradiance, images of J_t in air showed that photosynthesis decreased gradually, with this effect shifting from green to necrotic areas. Sudden increase in CO₂ concentration to 0·74% in the atmosphere around the leaf only partially reversed this inhibition, showing that both stomatal and metabolic inhibition occurred. Under limiting irradiance, decreases in J_t and in maximal J_t during high CO₂ exposure as leaf damage severity increased suggested that metabolic inhibition was mediated through an inhibition of Ribulose 1·5‐bisphosphate (RuBP) regeneration. Finally, the importance of our data in terms of assessing the loss of photosynthetic yield from visible symptoms – as is currently performed in epidemiology – is discussed.     

Somatic embryogenesis and plantlet regeneration in mango (Mangifera indica L.)

Summary The ‘Carabao’ or ‘Manila Super’ mango (Mangifera indica L.), a virtually neglected fruit before the advent of KNO₃ flower induction in the early 1970s, is now the third leading Philippine export fruit after banana and pineapple. To apply biotechnology for improvement, a reliable embryogenesis and regeneration protocol is required. We have developed a protocol for somatic embryogenesis and plantlet regeneration in mango: eight strains of ‘Carabao’ and two unidentified varieties, PHL 12384 and PHL 12378. Over 40 batches of nucellar explants from immature fruis (0.75–5.0 cm long) were cultured in vitro from April 1999 to April 2000. Two media were used, MMSE. Mango Medium for Somatic Embryo Induction, Proliferation and Germination and MMPR, Mango Medium for Plantlet Regeneration. These are now routinely used. The protocol is reproducible in 14 other varieties of mango. Shifting the base medium from Gamborg's B5 medium to our own formulation. BP medium (Barba and Pate?a's formulation) effectively controlled browning. Browning has limited the successful in vitro culture of many woody species including the mango. Crop Science Society of the Philippines (CSSP) 2001 Best Paper Award, Asian Agriculture Congress, Westin Philippine Plaza, Manila, Philippines, April 24–27, 2001 and Philippine Fruit Association 2000 Best Poster Award, 8th National Symposium. PCARRD, Los Ba?os, Laguna, Philippines, November 14–16, 2000.     

A historical review of research on the weaver ant Oecophylla in biological control

1 Although the weaver ant Oecophylla is the first written record of biological control, dating from 304 ad , there have been fewer than 70 scientific publications on this predator as a biological control agent in Asia, from the early 1970s onwards, and fewer than 25 in Africa. 2 Apart from crop‐specific ecological and perceptual factors, a historical review shows that political and market forces have also determined the extent to which Oecophylla was incorporated into research and development programmes. 3 In Africa, research on weaver ants in biological control concentrated on export crops, such as coconut and cocoa, whereas, in Asia and Australia, research focused on fruit and nut crops, primarily destined for domestic markets. 4 Increased evidence of pesticide inefficiency under tropical smallholder conditions, changing paradigm shifts in participatory research and a growing scientific interest in local knowledge in the early 1990s opened up new avenues for research on conservation biological control. 5 Lobbying and advocacy have been needed to ensure that Oecophylla was recognized as an effective biological control agent. 6 With an increased market demand for organic produce, holistic approaches such as conservation biological control, particularly the use of Oecophylla, are increasing in importance. 7 Multi‐stakeholder strategies for collaborative learning are proposed for a better control of major fruit, nut and timber tree pests in Africa, Asia and Australia.     

Plant regeneration of Mangifera indica using liquid shaker culture to reduce phenolic exudation

The exudation of phenolics from the cut ends of mango explants greatly hinders their regenerative ability in any in vitro growth medium. However, pretreatment of explants using liquid shaker culture helps in overcoming this problem. Explants kept in liquid MS medium supplemented with 1% polyvinylpyrolidone in 250 ml conical flasks on an automated shaker at 75 rpm were able to produce shoots when inoculated on gelled MS medium supplemented with different concentrations of growth regulators.Abbreviations BA benzyladenine - IAA indoleacetic acid - NAA naphthaleneacetic acid - IBA indolebutyric acid     

New records of mango shield scale Milviscutulus mangiferae (Green) (Hemiptera: Coccidae) and Brevennia rehi (Lindinger) (Hemiptera: Pseudococcidae) in north Queensland

Abstract  The first Australian records of mango shield scale ( Milviscutulus mangiferae ) from north Queensland and additional records from parts of Papua New Guinea are presented. The majority of specimens were collected from mango leaves ( Mangifera indica ). A summary of its known distribution, other hosts, identification and damage levels is also presented. Also, the detection of rice mealybug ( Brevennia rehi ) in far north Queensland is reported for the first time. This pest is known to occur in the Northern Territory. The north Queensland detections are from native grasses. The records presented here, for both species, are regarded as new detections, rather than new incursions.     

Evaluation of Water Yam (Dioscorea alata L.) Germplasm for Reaction to Yam Anthracnose and Virus Diseases and their Effect on Yield

Use of genetic resistance is the most practical and economic way to manage major diseases of yams. In a search for sources of resistance, 40 water yam (Dioscorea alata L.) accessions from Benin, Ghana, Nigeria and Puerto Rico were screened under natural disease infection conditions in Ibadan, Nigeria. The accessions were evaluated at 1, 3 and 6 months after planting (MAP) for severity of yam anthracnose and viral diseases. The effect of the pathogens on yield was also evaluated at harvest 9 MAP. There were significant differences (P < 0.001) between accessions for severities of anthracnose and viral diseases. Eight (20%) of them had lower anthracnose area under disease progress curves (AUDPC) values than the resistant check while 10 (25%) had AUDPC values below the trial mean. There were significant variations (P < 0.001) in yield components among the accessions. There was significant negative correlation of anthracnose severity with fresh tuber yield (r = −0.51) and with number of tubers per plot (r = −0.40). Similarly, significant negative correlations were observed of virus disease severity with fresh tuber yield (r = −0.78) and number of tubers per plot (r = −0.65). Linear regression models also showed that the fresh yield had significant negative relationships with anthracnose (R² = 0.26) and viral (R² = 0.62) diseases. The accessions identified as resistant constitute a valuable resource for breeding of resistant germplasm.     

Responses of embryogenic mango cultures and seedling bioassays to a partially purified phytotoxin produced by a mango leaf isolate of Colletotrichum gloeosporioides penz

Summary Colletotrichum gloeosporioides Penz., the causal agent of mango anthracnose, produces a phytotoxin in vitro. The partially purified phytotoxin, presumably colletotrichin, caused anthracnose-like symptoms on young mango leaves, was toxic to embryogenic suspension cultures of two mango cultivars, ‘Hindi’ and ‘Carabao,’ and inhibited in vitro seed germination of two nonhosts, lettuce and tobacco. There were linear relationships between concentration of the partially purified phytotoxin and mortality of mango embryogenic cultures. Embryogenic cultures grown in the presence of the partially purified phytotoxin showed significantly lower growth rates than the controls. Similarly, embryogenic cultures grown in the presence of 40% (vol/vol) fungal culture filtrate showed significantly lower growth rates than unchallenged controls. Medium containing 40% (vol/vol) Czapek-Dox fungal broth did not reduce growth of embryogenic cultures, indicating the production of phytotoxin in vitro. The results suggest that either fungal culture filtrate or purified phytotoxin can be used as in vitro selection agents to screen for resistance to this fungus.     

Marine yeasts and bacteria as biological control agents against anthracnose on mango

The potential of four yeasts (Debaryomyces hansenii, Rhodotorula minuta, Cryptococcus laurentii and Cryptococcus diffluens) and three bacteria (Bacillus amyloliquefaciens, Bacillus subtilis and Stenotrophomonas rhizophila) with antagonistic capacity against anthracnose caused by Colletotrichum gloeosporioides in mango cv. Ataulfo fruit was investigated. Germination of C. gloeosporioides spores was significantly inhibited by all marine yeasts and bacteria strains of an in vitro test. When yeasts and bacteria were tested on mango fruit, the marine yeast D. hansenii 1R11CB strain and marine bacteria S. rhizophilaKM02 strain were the best antagonists to anthracnose (C. gloeosporioides), which significantly decreased disease incidence by 56% and 89%, respectively, and reduced lesion diameter by 91% and 92%, respectively. All the isolated strains of the phytopathogen, yeasts and bacteria were molecularly identified. Our results from in vitro and in vivo experiments suggest that marine yeasts and bacteria strains can be used as some effective biological control agents for anthracnose in mango.     

Molecular Diversity and Assessment of Biological Characteristics of Greek Colletotrichum lindemuthianum Populations

Colletotrichum lindemuthianum  isolates collected in Greece were characterized by the temperature effect on their biological characteristics (mycelial growth, sporulation and spore germinability) and by molecular diversity revealed by RAM and ERIC–BOX PCR analysis. The temperature effect on the assessed biological characteristics resulted in a similar classification according to the origin and virulence patterns of isolates. Colletotrichum lindemuthianum isolates originating from the areas of Nevrokopi and Vrodou showed better adaptation at the lower temperatures exposure (12 and 18°C) compared to isolates originating from the Municipality of Hrisoupolis, which showed better adaptation at the highest temperature tested (24°C). Molecular diversity was detected using RAM and ERIC–BOX PCR primers. Both methods revealed, in a similar way ( r  = 0.58, P = 0.05), two main clusters of isolates, in agreement with previous findings using RAPD and RFLP analysis. The majority of the tested isolates were grouped in the same main cluster (29 out of 35 Greek isolates for both methods) underlying high levels of genotypic similarities between Greek populations of C. lindemuthianum . This study, an extension of previous research, provides further information on population diversity of C. lindemuthianum required for developing more efficient control strategies of bean anthracnose disease.