Apple Proliferation Resistance in Apomictic Rootstocks and Its Relationship to Phytoplasma Concentration and Simple Sequence Repeat Genotypes

Abstract

In an effort to select and characterize apple rootstock resistant to apple proliferation (AP), progenies from seven apomictic rootstock selections and their parental apomictic species, Malus sieboldii and M. sargentii, were compared to standard stocks M 9 and M 11. Seedlings derived from open pollinated mother plants were grafted with cv. Golden Delicious and grown under natural infection conditions. The progenies differed greatly in resistance to the AP agent 'Candidatus Phytoplasma mali'. Progenies of M. sieboldii and its descendent rootstock selections D2212, 4608, 4551, and D1131 showed a high level of resistance, whereas progenies of M. sargentii and its descendent selections D1111 and C1828 proved susceptible. M 9 and M 11 showed an intermediate level of resistance. Phytoplasma titer in roots of the M. sieboldii and M. sargentii progeny groups was similarly low, whereas the concentration in the standard stocks was 100 to 5,000 times higher. In trees on most of the resistant stocks, only a minority was colonized in the scion, while in trees on susceptible and standard stocks, infection rate was often higher. Also, the titer in the top of trees on resistant stocks was usually lower than in trees on susceptible and standard stocks. Four progenies derived from open pollinated M. sieboldii and M. sieboldii descendents were subjected to DNA typing using simple sequence repeat (SSR) markers. This study revealed that the selected groups consisted mainly of mother-like plants (apomicts) and type I hybrids (unreduced mother genotype plus one male allele at each locus). Type II hybrids (full recombinants) and autopollinated offspring were rare. In the 4608 progeny, trees grown on type I hybrid rootstocks were significantly less affected than trees on mother-like stocks. In other progenies with fewer or no type I hybrids, trees on type II hybrids and autopollinated offspring suffered considerably more from disease than trees on mother-like stocks.

Resistance Inducers and Plant Growth Regulators Show Only Limited and Transient Effects on Infection Rates, Growth Rates and Symptom Expression of Apple Trees Infected With ‘candidatus Phytoplasma mali’

“…Hundreds of thousands of infected trees were felled in the South Tyrol (Italy), the largest apple-producing area in the European Union, during the last decade, resulting in considerable economic damage. Apple rootstocks with increased resistance to AP were developed (Bisognin et al 2008), but due to unfavourable vigorous growth they are not suited for modern orchard production. Several recent studies indicate that application The phytoplasma titres were determined in July and October of 2009 and 2010, respectively.…”

Polymerase Chain Reaction for Phytoplasmas Detection

“…Phytoplasma pyri' (pear decline, PD), 'Ca. Phytoplasma pruni' (European stone fruit yellows, ESFY) important pathogens of fruit trees (12,76,48,156,3,4,113,23,128,41). Most of the primer/probe systems are targeting 16S rDNA gene though some others genes or even randomly cloned DNA fragments to which no specific function is assigned have been used (Table 3).…”

“…This approach was complex, several steps, such as electrophoresis, image analysis of gel, compensating for differences in intensity due to the different sizes of the product from the pathogen target and the internal standard, were required before the band intensities could be plotted for linear regression analysis. However, nowadays absolute quantification of phytoplasma DNA was achieved per gram of extracted tissue (161,23) or per insect vector (76). Possibility of the method to quantify amount of phytoplasma DNA in plant tissue and insect vectors gave opportunity to better understand biology and epidemiology of the pathogens, to allow examination of different multiplication rates and to calculate the concentration in their plant and vector host (161,142,23) as well as to study interactions of different phytoplasma species or strains present in mixed infection (100,19).…”

“…However, nowadays absolute quantification of phytoplasma DNA was achieved per gram of extracted tissue (161,23) or per insect vector (76). Possibility of the method to quantify amount of phytoplasma DNA in plant tissue and insect vectors gave opportunity to better understand biology and epidemiology of the pathogens, to allow examination of different multiplication rates and to calculate the concentration in their plant and vector host (161,142,23) as well as to study interactions of different phytoplasma species or strains present in mixed infection (100,19). These results will find application in development of resistant plant varieties, a hot topic for economically important woody crops such as palms, fruits and grapevines.…”

Apple proliferation resistance of Malus sieboldii-based rootstocks in comparison to rootstocks derived from other Malus species

“…They frequently develop symptoms, remain permanently infected and show, as estimated by DAPI (4′-6-diamidino-2-phenylindole) fluorescence staining and quantitative real-time PCR, high phytoplasma titers (Bisognin et al 2008;Seemüller et al 1992). …”