Stem cankers on sunflower (Helianthus annuus) in Australia reveal a complex of pathogenic Diaporthe (Phomopsis) species

Abstract

The identification of Diaporthe (anamorph Phomopsis) species associated with stem canker of sunflower (Helianthus annuus) in Australia was studied using morphology, DNA sequence analysis and pathology. Phylogenetic analysis revealed three clades that did not correspond with known taxa, and these are believed to represent novel species. Diaporthe gulyae sp. nov. is described for isolates that caused a severe stem canker, specifically pale brown to dark brown, irregularly shaped lesions centred at the stem nodes with pith deterioration and mid-stem lodging. This pathogenicity of D. gulyae was confirmed by satisfying Koch’s Postulates. These symptoms are almost identical to those of sunflower stem canker caused by D. helianthi that can cause yield reductions of up to 40 % in Europe and the USA, although it has not been found in Australia. We show that there has been broad misapplication of the name D. helianthi to many isolates of Diaporthe (Phomopsis) found causing, or associated with, stem cankers on sunflower. In GenBank, a number of isolates had been identified as D. helianthi, which were accommodated in several clades by molecular phylogenetic analysis. Two less damaging species, D. kochmanii sp. nov. and D. kongii sp. nov., are also described from cankers on sunflower in Australia.

Microbiological changes and severity of decay in apples stored for a long-term under different storage conditions

“…However, application of 1-MCP in organic farms is prohibited. Since organic growers stay away from synthetic fertilization and fungicide treatment, they have more intensive fruit decay that causes fruit yield losses (Tahir, 2006). The data found in the scientific literature suggest that Swedish organic orchard had 20% more apples damaged by microscopic fungi compared to conventional orchard (Jönssson et al, 2010).…”

“…Along with delaying ripening processes, respiration rate of fruits also can be suppressed; as a result fruit storability can be improved and quality maintained. Due to high carbon dioxide (CO 2 ) level in a storage room, antimicrobial properties of this compound can also be observed (Tahir, 2006).…”

“…Infection most commonly remains over winter on mummified fruits, on the ground, and in cankers. Infected fruits turn brown and soft (Tahir, 2006).…”

“…There is evidence that apples injured (peel and internal injuries) during harvesting will be susceptible to colonisation by P. expansum and P. digitatum pathogenic fungi (Tahir, 2006).…”

“…Another important storage technique that has great advantages is ultra low oxygen storage (JuhnevicaRadenkova et al, 2016). This type of storage is essentially based on delaying the ripening processes by controlling the level of gases around fresh fruits and vegetables (Tahir, 2006). Ultra low oxygen storage may substantially reduce the possible development of microorganisms and limit the possible infection of healthy fruits (Juhneviča et al, 2011).…”