First Report of a Bionectria sp. Associated with a Stem Rot of Cardon Cactus (Pachycereus pringlei) in Baja California Sur, Mexico

Abstract

Giant cardon (Pachycereus pringlei ((S.Watson) Britton & Rose) is the most common cactus in northwestern Mexico and is endemic to the Baja California Peninsula and Sonora Desert. A large part of the peninsula (El Vizcaino Biosphere Reserve and Gulf of California) now consists of protected areas and is classified as a World Heritage site by UNESCO ( http://whc.unesco.org/en/list/1182 ). Cardon cactus is an important ecological resource for indigenous people and is used as feed for range cattle. Since 2000, in the central and southern part of the State of Baja California Sur, an apical stem rot has spread to ~17% of the natural cardon population around San Pedro (23°29′N, 110°12′W), La Paz (24°08′N, 110°18′W), and El Comitán (24°05′N, 110°21′W). Affected cacti display necrosis of apical branches, dry rot, cracks in the stem and branches, bronzing of mature spines surrounding the affected area, and reddish brown gummy exudate. Thirty samples from the edges of symptomatic lesions were surface disinfected for 2 min in 0.8% (wt/vol) NaOCl and ethanol (70%), rinsed in sterile, distilled water, and grown on potato dextrose agar at 27°C. A cottony, brownish fungus was consistently isolated from affected tissues. Koch's postulates were performed in pots of 10 cm in diameter with 5-year-old cacti inoculated (9-day-old mycelia) and incubated (15 days) at room temperature (26°C). The rough, dry, brownish, circular lesions that appeared were the same as those observed in the field. Healthy cacti inoculated with potato dextrose agar plugs were symptomless. The fungus was always reisolated from infected cacti and morphological examinations (2) were performed: one-septate, olive-green, smooth, ellipsoidal conidium and two-celled ascospores (15 to 20 × 5 to 7 μm) were present. Also present were conidial masses from monomorphic, penicillate conidiophores in sporodochia. Cottony and white-to-light yellow PDA colonies were observed. Genomic DNA was extracted from lyophilized hyphae using the method described by O'Donnell (1) or with a DNeasy Plant Mini Kit (Qiagen, Hilden, Germany). The internal transcribed spacer (ITS) regions 1 and 2 of the 5.8, 18, and 28S ribosomal RNA genes were amplified with the primer pairs ITS1 and ITS4 (3). The expected amplicon of 571 bp was sequenced and compared with fungal sequences available from the GenBank-EMBL database using the BlastN and CLUSTAL programs (MegAlign, DNASTAR, Madison, WI). The closest nucleotide similarity had 99% identity with a Bionectria sp. (GenBank Accession No. HM849058.1). To our knowledge, on the basis of morphological characteristics, DNA comparisons, and pathogenicity tests, this is the first report of a Bionectria sp. causing an apical stem rot disease in cardon cacti in Mexico. Since there are no control measures in Mexico there is a permanent risk that the disease will spread to healthy areas. References: (1) K. O'Donell et al. Mycologia 92:919, 2000. (2) H. J. Schroers. Stud. Mycol. 46:1, 2001. (3) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, 1990.

Declined soil suppressiveness to Fusarium oxysporum by rhizosphere microflora of cotton in soil sickness

“…These findings are consistent with both cotton wilts being important constraints of production in the local cotton-growing areas. In addition, the abundances of S. chartarum, F. solani, A. sclerotigenum, P. decipiens, B. ochroleuca, F. merismoides, A. charticola, and F. equiseti were significantly increased in the cotton rhizospheres of monocropped soils, many of which are fungal plant pathogens (e.g., F. solani, B. ochroleuca, F. merismoides, and F. equiseti ) (Nayyar et al 2009;Holguín-Peña et al 2012;Xu et al 2012;Li et al 2014c). Content of sugars, phenolic acids, and amino acids in the root exudates of Zhong-38 (a) and NAU-10 (b) cotton seedlings grown on soils that had been cropped with cotton for 4 years (CC4) and for 15 years (CC15) and the fallow soil.…”

Asexual reproduction and vegetative growth of Bionectria ochroleuca in response to temperature and photoperiod

“…It has both sexual and asexual phases, and perithecia and conidiophores are formed in each phase, respectively (Schroers et al, 1999). It has been identified as a plant pathogen of several agrospecies (Bienapfl et al, 2012;Guesmi-Jouini et al, 2014;Holguín-Peña et al, 2012;Li et al, 2014), an endophyte (Samaga et al, 2014), or a free-living form (Kim et al, 2019). The change between these lifestyles is strongly influenced by environmental factors and plant defense responses (Schulz & Boyle, 2005).…”