Abstract
Lilium longiflorum cv. Nellie White, commonly known as Easter lily, is an important floral crop with an annual wholesale value of over $26 million in the United States. The root-lesion nematode, Pratylenchus penetrans, is a major pest of lily due to the significant root damage it causes. In this study, we investigated the cytological aspects of this plant-nematode interaction using bright-field and transmission electron microscopy. We took advantage of an in vitro culture method to multiply lilies and follow the nematode infection over time. Phenotypic reactions of roots inoculated with P. penetrans were evaluated from 0 to 60 d after nematode infection. Symptom development progressed from initial randomly distributed discrete necrotic areas to advanced necrosis along entire roots of each inoculated plant. A major feature characterizing this susceptible host response to nematode infection was the formation of necrosis, browning, and tissue death involving both root epidermis and cortical cells. Degradation of consecutive cell walls resulted in loss of cell pressure, lack of cytoplasmic integrity, followed by cell death along the intracellular path of the nematode's migration. Pratylenchus penetrans was never seen in the vascular cylinder as the layer of collapsed endodermal cells presumably blocked the progression of nematodes into this area of the roots. This study presents the first detailed cytological characterization of P. penetrans infection of Easter lily plants.
Highlights
The development of symptoms caused by P. penetrans in lily roots were characterized initially by randomly distributed discrete lesions or browning areas along the root tip and elongation zone, to well advanced necrotic areas along the entire root of the plant at more advanced time points (Fig. 1)
To follow up P. penetrans’ pattern of infection, nematodes were initially inoculated adjacent to the lily root tip, allowing the nematodes to migrate into the roots
The initial penetration site of P. penetrans in lily roots was mainly at the elongation zone, these nematodes seemed capable of penetrating lily roots in any part of the root, as nematodes were observed entering the entire root as disease and nematode development progressed
Summary
Among the approximately 80 species described so far for the genus Pratylenchus (Fosu-Nyarko and Jones, 2016), P. penetrans (Cobb, 1917) Filipjev and Schuurmans Stekhoven, 1941, is considered one of the most important species of this genus due to its large distribution, wide host range of at least 400 plants, and its impact on economically important crops (Castillo and Vovlas, 2007) Infestations of this species present a major problem in the production of bulb flower crops, such as lily plants. Characterized in detail the mechanism of infection and general cell phenotype response of lily roots to P. penetrans infection
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