Incidencia de la procesionaria del pino, Thaumepotaea pityocampa Denis & Schiffermüller, 1775 en masas forestales de Pinus nigra salzmannii (Dunal) Franco, 1943 y su relación con variables ambientales

El Pinus nigra salzmannii es una subespecie relicta del pino negral presente en la región mediterránea de la Península Ibérica localizada, fundamentalmente, en forma de masas aisladas de las cotas superiores de diversas elevaciones montañosas. El parásito fitófago Thaumopotaea pityocampa se alimenta de este árbol durante su estado larvario, provocando daños apreciables en el estado fitosanitario de los árboles. En este estudio se ha medido la incidencia del parásito sobre los árboles del Parque Natural de Sierra Magina y su relación con variables bióticas y abióticas; para ello se ha realizado un muestreo en transecto empleando la medida de la distancia al vecino más próximo como un estimador de la densidad de la masa forestal, distinguiendo entre dos zonas de bosque estructuralmente diferentes, una con los árboles en distribución más abierta, y otra de bosque cerrado. Los resultados confirman la hipótesis de que se produce un número significativamente mayor de infecciones en bosque abierto y que está afección diferencial está relacionada con las diferencias estructurales de los dos tipos de bosque. Además, para el hecho de que los árboles en bosque abierto se vean más afectados, se plantea la hipótesis de que se deba a la ecología de la larva de la procesionaria con respecto a la temperatura a la que esta sobrevive, siendo requeridos posteriores estudios para confirmar dicha hipótesis. Para las variables bióticas y abióticas no se han encontrado relaciones significativas con la incidencia del parásito

Morphological and molecular characterisation of Scutellonema species from yam (Dioscorea spp.) and a key to the species of the genus

The yam nematode, Scutellonema bradys, is a major threat to yam (Dioscorea spp.) production across yam-growing regions. In West Africa, this species cohabits with many morphologically similar congeners and, consequently, its accurate diagnosis is essential for control and for monitoring its movement. In the present study, 46 Scutellonema populations collected from yam rhizosphere and yam tubers in different agro-ecological zones in Ghana and Nigeria were characterised by their morphological features and by sequencing of the D2-D3 region of the 28S rDNA gene and the mitochondrial COI genes. Molecular phylogeny, molecular species delimitation and morphology revealed S. bradys, S. cavenessi, S. clathricaudatum and three undescribed species from yam rhizosphere. Only S. bradys was identified from yam tuber tissue, however. For barcoding and identifying Scutellonema spp., the most suitable marker used was the COI gene. Additionally, 99 new Scutellonema sequences were generated using populations obtained also from banana, carrot, maize and tomato, including the first for S. paralabiatum and S. clathricaudatum, enabling the development of a dichotomous key for identification of Scutellonema spp. The implications of these results are discussed

Distribution, prevalence, and severity of damages caused by nematodes on yam (Dioscorea rotundata) in NIssathme30igeria

Nigeria is the main yam-growing country of the world. In the country, various plant-parasitic nematodes have been reported constraining yam production and the storability of tubers. This study established the damage level of nematodes on white yam tubers (Dioscorea rotundata) across the major production areas in the country for management purposes. Incidence and severity of symptoms (cracking, dry rot, and galling) associated with nematodes were assessed on 1,114 yam heaps (181 vendors) from 23 markets and on 2,502 tubers from 26 farmer storage areas (yam barns) in the Humid Forest (HF), Derived Savanna (DS) and Southern Guinea Savanna (SGS) agro-ecological zones (AEZ). On yam heaps, the symptom incidence averaged 55%, 35%, and 6% for galls, dry rot, and for cracks, respectively. Only the incidence of dry rot was significantly different (P<0.0001) across the AEZ. On yam tubers, the incidence averaged 24%, 8%, and 2% for galls, dry rot, and for cracks, respectively. The incidence for galls was higher in the SGS than in the DS (P=0.0018) whereas the incidence of cracks was higher in the DS than in the SGS (P=0.0080). The actual values of symptom severity were, in general, low in the AEZ compared with the predicted values except for dry rot. A significant positive correlation was found between galls and Meloidogyne and between dry rot and Scutellonema. Pratylenchus was also recovered from a few yam tubers; however, no link with symptoms on yam tubers could be established. Vendors and farmers, based on the answers from a questionnaire, were very familiar with nematode symptoms on yam tubers, but awareness of nematodes was low. This study shows that Meloidogyne and Scutellonema are the major nematode constraints to yam production in the three AEZ of Nigeria and calls for effective yam nematode management in Nigeria and in other yam-producing countries

A report of Meloidogyne arenaria Parasitizing Plantain (Musa spp., AAB) in Nigeria

Extensive root galling observed on plantain (Musa spp., AAB) in Nigeria was analysed using Nad5 mitochondrial DNA sequences and the causal agent identified as Meloidogyne arenaria. Following the inoculation of population cultured, Koch's postulates was fulfilled and the same symptoms observed. This provides the first molecular confirmation of M. arenaria causing such damage to plantain and highlighting its potential as a threat to the crop. Root knot nematodes are known to affect banana and plantain production but diagnosis of the species involved is only just being accurately determined with the recent improvements in molecular techniques

An improved phenotyping method for evaluation of Yam (Dioscorea spp.) resistance to nematodes belonging to the Genera Meloidogyne and Scutellonema

Phenotyping yam (Dioscorea spp.) germplasm for resistance to parasitic nematodes is hampered by the lack of an efficient screening method. In this study, we developed a new method using rooted yam vine cuttings and yam plantlets generated from semi-autotrophic hydroponics (SAHs) propagation for phenotyping yam genotypes for nematode resistance. The method was evaluated using 26 genotypes of D. rotundata for their reaction to Scutellonema bradys and four root-knot nematode species, Meloidogyne arenaria, M. enterolobii, M. incognita, and M. javanica. Yam plantlets established in nursery bags filled with steam-sterilized soil were used for screening against single nematode species. Plants were inoculated four weeks after planting and assessed for nematode damage eight weeks later. A severity rating scale was used to classify genotypes as resistant, tolerant, or susceptible determine based on the nematode feeding damage on tubers and the rate of nematode multiplication in the roots of inoculated plants. The results demonstrated putative resistance and tolerance against S. bradys in 58% of the genotypes and 88%, 65%, 65%, and 58% against M. arenaria, M. javanica, M. incognita, and M. enterolobii, respectively. The method is rapid, flexible, and seasonally independent, permitting year-round screening under controlled conditions. This method increases the throughput and speed of phenotyping and improves the selection process