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 Add this item to the list  Phytophthora pini Leonian, 1925
   
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Page number:355 
Remarks (internal):Phytophthora pini is resurrected to distinct species status. Phylogenetically P. pini is in a terminal cluster different from P. citricola s.s. and all other species recently segregated from this species complex. P. citricola s.s. and P. pini are similar morphologically. They both have globose oogonia about 30 µm diam and plerotic oospores with walls about 1.5-1.7 µm thick. Their antheridia however are different, particularly in size and shape. Those of P. pini are larger, 11.1 µm tangential to the oogonial wall and 12.6 µm perpendicular to the wall, whereas those of P. citricola s.s. are round and 10 µm or less diam. Also the antheridia of P. pini are capitate, usually slightly asymmetrical. In addition P. pini formed a few small hyphal swellings and occasional clumps of irregular hyphae, whereas P. citricola s.s. did not. Physiologically P. pini grew more quickly than P. citricola s.s.
Phytophthora citricola I (Kong et al. 2003, Gallegly and Hong 2008) is formally replaced with P. pini because they are phylogenetically, morphologically and physiologically identical. The holotype was deposited by Leonian, and the name P. pini should take precedence over other names, although a Latin description was not given and was not required before 1935. Our emended description includes a Latin description of the ex-holotype of ATCC 64532 and CBS 181.25. This isolate is listed under subgroup CIT1 (2) (Oudemans et al. 1994). It must be pointed out that isolates CIT-US1 and CIT-US10 are more closely related to P. citricola III than P. pini (= P. citricola I) in the cox1 tree, although both were placed in the same group by the ITS sequences (Jung and Burgess 2009). Several differences in temperature response was observed between P. pini in the present study and both isolates (CIT-US1 and CIT-US10) (Jung and Burgess 2009): (i) the optimum temperature of 25 C vs. 30 C and (ii) average daily radial growth rates of 7.0 vs. 9.2 mm. These differences along with others (Hong et al. unpubl data) support P. citricola III as a separate taxa (Gallegly and Hong 2008).
Phytophthora pini is readily established in North America and Europe as a pathogen on plants in seven genera. This species also could attack a variety of other ornamental and vegetable plants (Hong et al. 2008) and European beech trees (Jung et al. 2005). It is likely that many isolates identified as P. citricola s.l. in major culture collections in reality are P. pini or P. plurivora. Similarly many plant species currently listed as hosts of P. citricola s.l. (Farr et al. 2009) might be hosts of P. pini instead. Much work will be needed to elucidate the host ranges of P. pini and other emerging entities from P. citricola s.l.
Phytophthora pini poses a growing threat to the horticulture industry for several reasons. P. pini favors alkaline aquatic environments with the optimum pH of 9 (Kong et al. 2009). This occurs in most agricultural runoff containment basins/irrigation reservoirs for most of the growing season (Hong et al. 2009b). This species consequently has been recovered frequently from irrigation reservoirs and natural waterways in Virginia; some isolates of which were identified as P. citricola s.l. or P. citricola I (Bush et al. 2003, Bush et al. 2006, Ghimire et al. 2009). Considering global water scarcity, the horticulture industry increasingly depends on recycled water for irrigation (Hong and Moorman 2005). Accordingly the risk of this species accumulating and being redistributed through recycling irrigation systems is expected to rise. In addition P. pini was the only species among the 18 isolates from 12 species tested that can establish itself in media without soil (Hong et al. 2008). Thus it is important to monitor this species closely and take it into consideration in crop health management planning. To this end this study will help put vital research on the right track (Grovers 2001) and improve the accuracy of plant disease diagnostic services.
 
Description type:Non-original description 
Description:Phytophthora pini Leonian, 1925
Emend. Gallegly, Hong, Richardson & Kong
= Phytophthora citricola I Gallegly & Hong 2008
Morphology. - Phytophthora pini is homothallic with paragynous antheridia. Oogonia produced on clarified V8 agar are globose and relatively uniform, averaging 30.3 µm diam (range 22.2-41.4 µm diam). Oospores are mostly plerotic and average 26.0 µm diam (19.6-34.2 µm diam), their cell walls are 1.7 µm thick (1.4-1.9 µm). The antheridial characters differ from those of P. citricola s.s. The antheridia are larger, capitate to slightly asymmetrically capitate, diclinous, and attached at the base near the oogonial stalk. Occasionally two antheridia per oogonium may be seen. Antheridia are 11.1 µm tangential to the oogonial wall (range 10.2-12.9 µm) and 12.6 µm perpendicular to it (10.2-15.0 µm). The noncaducous semipapillate sporangia are mostly ovoid. However ellipsoid, bluntly ellipsoid and bizarre shapes occur in 10% soil extract. Sporangia averages 47.4 x 31.5 µm (l/b ratio is 1.52 and the range is 31.5-75.3 x 21.7-49.5 µm). Major character differences were observed among the four isolates assessed (supplemental table III).
Dimensions of sexual structures produced on hempseed agar average 30.1 µm for oogonia, 26.5 µm for oospores and 1.7 µm for oospore wall. These measurements are comparable to those on clarified V8 agar. Sporangia produced on lima bean agar are 56.8 µm long and 36.6 µm wide, larger than those on clarified V8 agar. First-flush sporangia are larger and tend toward being ellipsoid, whereas sporangia produced later are smaller and ovoid. Simple sympodia occur, sometimes close but mostly loose. Chlamydospores have not been seen, but a few small hyphal swellings and irregular hyphae sometimes occur in lima bean agar (fig. 2).
Holotype =VTMH11737 (ATCC 664532, CBS 181.25, IMI 77970)
 
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