Bud Rot Caused by Phytophthora palmivora: A Destructive Emerging Disease of Oil Palm

Oomycetes from the genus Phytophthora are among the most important plant pathogens in agriculture. Epidemics caused by P. infestans precipitated the great Irish famine and had a major impact on society and human history. In the tropics, P. palmivora is a pathogen of many plant species including cacao (Theobroma cacao), citrus (Citrus sp.), durian (Durio zibethines), jackfruit (Artrocarpus heterophyllus), rubber (Hevea brasiliensis), and several palm species including coconut (Cocos nucifera), and the African oil palm (Elaeis guineensis) as determined recently. The first localized epidemics of bud rot in oil palm in Colombia were reported in 1964. However, recent epidemics of bud rot have destroyed more than 70,000 ha of oil palm in the Western and Central oil palm growing regions of Colombia. The agricultural, social, and economic implications of these outbreaks have been significant in Colombia. Identification of the pathogen after 100 years of investigating the disease in the world enabled further understanding of infection, expression of a range of symptoms, and epidemiology of the disease. This review examines the identification of P. palmivora as the cause of bud rot in Colombia, its epidemiology, and discusses the importance of P. palmivora as a major threat to oil palm plantings globally.

Origin of the subepidermal tissue in Piper L. leaves

Studies on the anatomy of Piper leaves demonstrate the presence of a subepidermal tissue distinct from the adjacent epidermis, which cells show thin walls and hyaline contents. Some authors consider such cells a hypodermal tissue, while others refer to them as components of a multiple epidermis. In this study, the nature of this subepidermal tissue was investigated through the analysis of leaf ontogeny in three Piper species. The analysis showed that the referred tissue originates from the ground meristem and, thus, should be considered a hypodermis. The studied species suggests that the role of the hypodermis would be to protect the photosynthetic apparatus from excess light, regulating the intensity of light reaching the chlorophyll parenchyma.

First Report of Bud Rot Caused by Phytophthora palmivora on African Oil Palm in Colombia

A bud rot disease, referred to as "pudricion del cogollo" or PC (for its name in Spanish), is a major disease of oil palm in four production areas of Colombia. Even though the disease has been studied for more than 40 years in Central and South America, the causal agent remained unknown (1). Infection first develops in the palm heart (cogollo) above the meristematic zone. Initial external symptoms appear as necrotic lesions on the sides of the spear leaf (youngest, unexpanded leaf) and the sizes of the lesions remain static as tissues emerge, expand, and mature. Under favorable environmental conditions (temperature around 26°C and relative humidity above 80%), further rotting of the heart eventually destroys the bud. A baiting technique with papaya and cocoa fruits was successfully used to trap the causal agent from symptomatic spear leaf tissue collected from the provinces of Nariño and Santander (2), where the disease is severe. Small, triangular-shaped pieces were removed from healthy fruits that had been surface sterilized, and a corresponding piece of diseased oil palm tissue was inserted into the hole and sealed with the removed fruit tissue. The whole fruit was wrapped with plastic and incubated at 25°C. Once the fruit traps showed initial necrotic symptoms, fruit tissue from the advancing point of the lesions was plated on Phytophthora-selective media. Four isolates of Phytophtora palmivora, all A2 mating type, were obtained during this study and each presented similar white and depressed mycelium when grown on oatmeal agar (OMA) medium. Papillated, ellipsoidal sporangia with short pedicels had an average size of 37.1 (breadth) × 52.8 μm (length). Chlamydospores averaged 35.1 μm in diameter and were similar to those observed in diseased palm tissue. DNA from the Phytophthora isolates was used as a template for PCR using ITS1/ITS4 primers. BLASTn analysis of the ITS sequences (GenBank Accession No. GQ398157) showed 99.9% homology with P. palmivora. The sequences of the four isolates were identical. For pathogenicity testing, cultures were grown on OMA. Two milliliters of distilled water containing 40,000 sporangia were injected into the base of the spear leaf of 105 nursery palms; the same number of palms was injected with 2 ml of distillated water as controls. Initial PC symptoms were observed 3 to 4 days after inoculation on 85% of inoculated palms and 15% of these palms developed typical bud rot symptoms under favorable conditions. No symptoms were observed on the controls. The presence of Phytophthora was confirmed by light microscopy and P. palmivora was reisolated from symptomatic palms with the fruit-baiting technique. The presence of Phytophthora in the four Colombian growing areas was also confirmed using Agdia (Elkhart, IN) immunostrips followed by DNA extraction from the Immunostrip wick and ITS sequencing to confirm the species. To our knowledge, this is the first report of P. palmivora causing PC on oil palm in Colombia. References: (1) H. de Franqueville. Exp. Agric. 39:225, 2003. (2) G. Sarria et al. Rev. Palmas, Colombia. 29(3):31, 2008.

Karyotypic studies of Cratylia argentea (Desv.) O. Kuntze and C. mollis Mart. ex Benth. (Fabaceae - Papilionoideae)

Cratylia argentea and C. mollis (Fabaceae-Papilionoideae) are legume shrubs native to the Cerrado and Caatinga, respectively. Both species show great resistance to drought and high nutritive value, which makes them a valuable forage resource in tropical regions. Cytogenetic studies were carried out on accessions of C. argentea and C. mollis from Germplasm Banks of Embrapa Gado de Leite (Juiz de Fora, MG) and Embrapa Semi-Arido (Petrolina, PE), respectively. Root tips were treated with 3 mM 8-hydroxyquinoline and slides were made using the air-dry technique. Karyotype description for each accession took into account the following features: chromosome number; total length, relative length and arm ratio of each chromosome; haploid set length, and degree of asymmetry. Mitotic metaphases in both species showed 2n = 22 chromosomes, where this is the first report of diploid number for C. mollis. Chromosome length was also quite similar for the two species, ranging from 5.08 to 2.50 microm in C. argentea and 5.12 to 2.51 microm in C. mollis, with haploid sets of equal size, measuring 38.10 and 37.85 microm, respectively. However, they did not show the same karyotypic formula, which was 5 m + 4 sm + 2 st for C. argentea and 7 m + 2 sm + 2 st for C. mollis. This indicates the occurrence of rearrangements within chromosomes I and VI. Both karyotypes showed a tendency for asymmetry.