Effects of pH and titratable acidity on the growth and development of Monilinia laxa (Aderh. & Ruhl.) in vitro and in vivo.

Abstract

This investigation examines the effects of pH and titratable acidity on the growth and developments of a strain of Monilinia laxa (Aderhold & Ruhland) at seven different pH levels in Potato Dextrose Agar media and on peach fruit from formation to commercial maturity. The fungi growth was obtained by daily measurement of mycelia on the pH amended Potato Dextrose Agar. The sporulation performance was determined after 30 days of culture incubation. Fruits were inoculated with M. laxa, from fruit set to maturity, on weekly basis for brown rot susceptibility. The pathogen development, in vitro, was affected, by the pH (2.4-11.52) amended nutrient media. M. laxa exhibited variation in its growth and sporulation capacities on the seven pH amended PDA, preferring relatively moderate acidic conditions for optimum performance. In the in vitro analysis, there was mycelia growth at pH 2.40 to 8.84, while pH 11.52 did not support any mycelia growth. There was a continuous and stable increase in weight of fruit as it developed whereas the fruit size increased, then decreased and finally increased as the fruit develops. The acidity dynamics exhibited a non-sinusoidal waveform through the growth and development of the fruit. In all these characteristic variations, M. laxa did not develop infection or shown any brown rot incidence in the fruit until the period of commercial maturity.

Peach Brown Rot: Still in Search of an Ideal Management Option

“…is variable throughout fruit development. The susceptibility is high during the early stages of fruit development, decreases during the green fruit or pit hardening stage, and increases again during the ripening period [8,34]. Phenologically, peach fruit development generally undergoes four stages (S-I to S-IV, Figure 2f-g) from flowering to maturation: Fruit set (S-I), characterized by cell division and elongation, also referred to as the exponential growth phase; pit hardening (S-II), when the endocarp hardens to form the stone and scarcely increases the fruit size; pre-climacteric phase (S-III), which is another exponential growth phase, with a resumption of rapid cell division and fruit size enlargement; the climacteric stage (S-IV), with final cell division, cell expansion, and ripening/maturation [35,36].…”

“…(position in classification: Sclerotiniaceae, Helotiales, Leotiomycetidae, Leotiomycetes, Pezizomycotina, Ascomycota) [42]. The species of Monilinia are among the major causal organisms of brown rot disease in various orchard tree crops including: (a) Stone fruits [4,40,41,43,44], such as apricots [45,46], peaches [5,8,47,48], nectarines [48], cherries [49], and plums [45]; (b) Almonds [50] occasionally; and (c) Some pome fruits [51,52], such as pears [51], apples [53], and quinces [54].…”

“…Then, the brown rot disease cycle continues as indicated in Figure 5. However, when conditions (weather) are unfavorable, the infection can remain latent [72] until fruit maturity, the optimal time of disease development [8,57,73].…”

“…This biological proficiency conversely causes a grave impairment of the harvest, storage, and commercial shelf life of the product [87,108]. Interestingly, as it is found in any pathogen-host association, the growth and development of brown rot is influenced by different physicochemical conditions, such as temperature and water activity [109], light, aeration and pressure [110], pH, and titratable acidity of the fruits [8,111,112].…”

“…In peach fruits, acidity is an important genetic quality trait [113] which influences both perception of sourness and sweetness found in varying proportions depending on the cultivar and the ripening stage [115]. The influence of pH and TA on fungal-host interactions is documented [8,116]. Some fungal species prefer neutral to slightly alkaline conditions [110].…”