Studies On Nutritional Physiology Of Phytophthora Sojae And Biological Characteristics Of A Slowly-growing Isolate

Phytophthora sojae Kaufmann et Gerdemann is one of the most important plant pathogenic oomycetes with strong parasites and enormous economic damage on soybean. Effects on vegetative and sexual reproduction under different nutrition conditions of P. sojae were researched systematically in this dissertation, including effects of different mediums, carbon and nitrogen sources, microelements, animal hormone progesterone on mycelial growth rate, oospore production and some other characteristics of P. sojae. The culture characteristics, pathogenicity, transmission rule and some other biological characteristics of an slowly-growing P. sojae isolate HN-1discovered in the former research was also studied in this dissertation. The main results were as follows.1Effects of different mediums on mycelial growth and oospore production of P. sojaeThe effects of different mediums on the mycelial growth and oospore of P. sojae were studied. The results showed that the mycelial growth rate on different mediums of the tested isolate AH is OMA,MA＞LBA＞10%V8＞CA＞TA＞SBA＞PDA in turn to isolate SD, it is OMA,MA＞TA＞LBA=CA＞10%V8＞SBA＞PDA OMA＞MA＞10%V8＞LBA＞TA＞CA＞SBA＞PDA for isolate HN-1and OMA,MA＞TA＞LBA＞10%V8＞CA＞SBA＞PDA when it comes to isolate HN-2. Oospore production on different mediums of the tested isolates is10%V8＞LBA＞OMA＞MA＞SBA＞TA＞CA＞PDA,10%V8＞LBA＞OMA＞TA＞SBA=MA＞CA＞PDA,10%V8＞LBA＞CA＞SBA＞TA＞OMA＞MA＞PDA,10%V8＞CA＞SBA＞LBA＞OMA＞TA＞MA＞PDA in turn, for AH, SD, HN-1and HN-2separately. There is no correlation between those two characteristics. Correlation analysis shows that different isolates have different nutritional needs on vegetative and sexual reproduction.10%V8、LBA are suitable mediums while PDA unsuitable for their growth.2Effects of different carbon and nitrogen sources on mycelial growth of P. sojaeThe effects of artificial mediums with different carbon and nitrogen sources on mycelial growth of P. sojae isolate HN-2were studied. The results showed that colony diameter on medium with maltose is the biggest one which was more than90mm, next was sucrose, glucose and fructose in turn，their diameters reached73.67mm,68.67mm, and56.83mm separately. Soluble starch could not be made of good use as the diameter was41mm, carbon-free CK’s diameter was the least, just20.33mm. Diameter on medium with maltose is the biggest one which had reached68.67mm, next was urea, inorganic nitrogen could not be made good use of the isolate tesed, as diameters on mediums with sodium nitrate, ammonium sulfate, ammonium chloride were26.5mm,17.5mm and16.17mm separately. Nitrogen-free CK’s diameter was42mm. It shows that isolate HN-2can make use of both monosaccharide and polysaccharide, it prefer organic nitrogen compared with inorganic nitrogen.3Effects of microelements on mycelial growth of P. sojaeThe effects of different microelements on mycelial growth of P. sojae isolate HN-2were studied. The results showed that colony diameter on medium with50μg/L B³⁺ was the biggest which had reached56.50mm, next was Mo⁶⁺, Mn²⁺, Zn²⁺ in turn, the colony diameters was56.00mm、54.50mm and53.00mm separately. Colony diameter on medium with compound microelements was51.50mm, as microelement-free CK’s diameter was48.33mm. Colony diameters on mediums with50μg/L Co²⁺, Cu²⁺, Fe²⁺ was39.17mm,35.00mm and26.17mm separately. Shows that50μg/L B³⁺, Mo⁶⁺, Mn²⁺, Zn²⁺ could improve the vegetative growth of P. sojae isolate HN-2, however,50μg/L Co²⁺, Cu²⁺, Fe²⁺ may inhibit the growth of the isolate tested.4Effects of animal hormone on mycelial growth and oospore production of P. sojaeThe effects of animal hormone progesterone in different densities on mycelial growth and oospore production of P. sojae isolate HN-2were studied. The results showed that the mycelial growth and oospore production were largely influenced by progesterone in different densities. colony diameter on medium without progesterone was just23.25mm, while add progesterone in the medium to20,40,60,80mg/L could increase the colony diameter to34.5,33.5,32.5,30.5mm separately, the thickness of the colonies also increased. Oospore production had been improved when add progesterone into the medium, oospore production was140,220,140,60per mL separately as the density from20mg/L to80mg/L. The results above-mentioned showed that animal hormone progesterone in low density could improve both vegetative and sexual reproduction of the isolate tested.5Transmission rule of the slowly-growing P. sojae isolate HN-1The culture characters and pathogenicity of slowly-growing isolate HN-1of Phytophthora sojae and its single-zoospore progeny were observed and measured, and the transmission rules and culture characters, pathogenicity of the infected cultures from HN-1were researched through dual culture with other3normally-growing isolates. The results showed that the slowly-growing isolate HN-1of Phytophthora sojae had significant difference on culture characters，growth rate and oospore production compared with normal-growing isolates. HN-1was confirmed to be weak pathogenic isolate through inoculation in vivo. The characteristic of slowly-growing of HN-1could be transferred to normal-growing isolates and the cultures through hyphal contact expressed slowly-growing characteristic and their pathogenicity were weakened.