Phytophthora infestans Resistance in Tomato

The assignment discusses the emergence of late blight in tomato production worldwide and the importance of detecting resistance genes through QTL analysis and molecular marker studies. It highlights the use of RFLPS linkage maps for identifying resistance QTLs on tomato chromosomes, which suggests functional conservation with earlier charted QTLs and R genes in potato. The document also references various research papers that have successfully detected resistance genes in tomatoes against Phytophthora infestans and other diseases such as Tomato yellow leaf curl virus and verticillium wilt.

Running head: GENOMIC DISEASE RESISTANCE TO LATE BLIGHT OF TOMATO
Genomic Disease Resistance To Late Blight Of Tomato
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1GENOMIC DISEASE RESISTANCE AGAINST LATE BLIGHT OF TOMATO
Tomato or Solanum lycopersicum is a very vital vegetable crop in the world.
According to the recent estimation, about 4.6 million ha of tomatoes are grown per year
around the world, producing over 126million mt (Straquadine, Baig and Mukhtar 2017).
Apart from being the second most important vegetable crop, tomatoes are also considered as
a model species of plant for many of the genetic studies associated with stress tolerance, fruit
quality or several other psychological traits. Furthermore, to meet with the demands for
tomatoes, they are also grown in the greenhouse. Due to great economic contribution of
tomatoes in the field of agriculture, there is plentiful interest in making use of the genomic
tools in order to ameliorate the tomato and grow more new varieties of it.
May times, the production of tomatoes are hindered by several fungal diseases such as
late blight, fusarium wilt, early blight, verticilium wilt, septoria leaf spot, etc (Ohara et al.
2015). Among all; the late blight is the most critical one. It is one of the most vital foliar
fungal disease in tomatoes. It is the same fungus, which created the destructive loss of
potatoes in the year 1845 in Europe. It limits the tomato production. Late blight of tomato is
considered as one of the most infamous diseases in the field of agriculture (Jung et al. 2015).
It is acclaimed as the root of the famous Irish potato famine of the mid nineteenth century
that has resulted in the demise of more than two million people in Ireland. The disease in fact
spurred the exposure of the study of plant pathology. During his studies to understand the
root cause of late blight, Anton deBary, the botanist demonstrated that a fungal-like growth
on the blighted plants was the reason behind it. This had led other scientists and botanists to
investigate on other bacteria and fungi that were related to plant diseases and along with the
expansion of the Koch’s postulates for initiating pathogenicity, causal pathogens of several
plant diseases have been identified.
The late blight is originated by oomycete pathogen called the Phytophthora infestans
(Zuluaga et al. 2016). It in fact is fundamentally a pathogen of tomatoes and potatoes.

2GENOMIC DISEASE RESISTANCE AGAINST LATE BLIGHT OF TOMATO
However, it has also been known to infect the other adherents of the plant family of
Solanaceae. It is also significant for having both sexual and asexual life. However, the
disease is also referred to as community disease as it has the ability to circulate or spread
speedily from one field to another under right weather conditions. It is mostly favored by
humid, foggy or raining conditions and cool temperature. It quickly ruins the entire crop and
supplies a good source of infections for the other plants. Hence, it is very important for the
gardeners to understand the fact that the disease of tomato late blight is not like the other
usual tomato diseases. The other diseases causes very limited damage but Late blight in fact,
kills the plants completely and is highly infectious and communicable.
Late blight is one of the known destructive diseases of tomatoes in the world. Because
of the emergence of the very new and aggressive isolates of Phytophthora infestans,
identification of new genomic diseases resistance to Late Blight is a top most priority in
breeding of tomatoes. The term ‘phytophthora’ is a Latin term, which means ‘plant destroyer’
(Lazebnik et al. 2017). The tissues of the infected plants die and the outbreak grow and
spread rapidly as the pathogen has the ability to produce a large number of wind-dispersed
spores. If once a plant gets infected, it is bound to destroy. Its occurrence in a garden may
even affect the other gardens as well and this is due to wind dispersion of the spores.
From the popular Irish famine, there has been a high amount interest of the
researchers in the disease of late blight. At first, it they studied the affect of the same in
potatoes but later the study was held in tomatoes as well. The three major genetic disease
resistances against LB include Ph-1, Ph-2 and the Ph-3 (Luan et al. 2018). These resistances
have been charted to the tomato chromosomes 7, 10 and 9 respectively. The Ph-1 is a single
dominant gene that provides resistance in order to trace the race T-0, but it was speedily
mastered by the new races of pathogen. It was portrayed to the very distant end of the
chromosome 7 by making use of morphological markers but it has been reported that there

3GENOMIC DISEASE RESISTANCE AGAINST LATE BLIGHT OF TOMATO
was no molecular marker that was related with this resistance gene. The Ph-2 on the other
hand is a single insufficient-dominant gene that was portrayed to the very lower end of the
prolonged arm of the tomato chromosome 10. It supplies limited resistance to various isolates
of the race T-1. Ph-3 was primarily discovered in the accessions of S. pimpinellifolium-
L3708 and L3707 in Taiwan (Siedl Johnson, Jordan and Gevens 2014). At present, Ph-3 is
the most useful among the three major genetic disease resistances. It benefits insufficient
dominant resistance against wide array of Phytophthora infestans tomato isolates including
the ones that overcomes both Ph-1 and Ph-2. It has been portrayed to the very lower end of
the prolonged arm of the tomato chromosome 9 and near the RFLP marker- TG591. Ph-3 has
been portrayed in the 0.5cM genomic area of the long arm of chromosome 9 in between the
P55 and Indel_3 molecular markers.
In addition to these, there are several reports on the quantitative resistance to the late
blight as well as the QTLs (Quantitative trait loci) that are related to it. In a study, the
reciprocal backcross (BC) populations that are derived from the Solanum habrochaites x
Solanum lycopersicum were evaluated by using three kinds of copied disease essays i.e.
whole-plant, field and detached-leaflet (Haggard, Johnson and Clair 2015). The linkage maps
were developed for each of the BC population by making use of RFLPS. The resistance
QTLs was spotted on all of the twelve tomato chromosomes by using interval mapping.
Some of the Phytophthora infestans resistance QTLs were identified in the tomato tallied
with the chromosomal locations of earlier charted QTLs and the R genes in potato for
resistance to Phytophthora infestans, which suggests functional conservation of the resistance
in the Solanaceae.
Tomato is the one of the most consumed vegetable crops in the world but the
emergence of the late blight is considerably limiting its production worldwide. The QTL
analysis and the molecular markers analysis works that are executed so far has been very

4GENOMIC DISEASE RESISTANCE AGAINST LATE BLIGHT OF TOMATO
competent for detecting the resistance gene or genes on the genome of the tomatoes and to
accomplish marker-assisted choice for few fungus related diseases. As the whole genome
succession of tomato is available now, it will be very useful for advancing the molecular
breeding through smoothing the positional cloning and marker-assisted selection.

5GENOMIC DISEASE RESISTANCE AGAINST LATE BLIGHT OF TOMATO
References:
Haggard, J.E., Johnson, E.B. and Clair, D.A.S., 2015. Multiple QTL for horticultural traits
and quantitative resistance to Phytophthora infestans linked on Solanum habrochaites
chromosome 11. G3: Genes, Genomes, Genetics, 5(2), pp.219-233.
Jung, J., Kim, H.J., Lee, J.M., Oh, C.S., Lee, H.J. and Yeam, I., 2015. Gene-based molecular
marker system for multiple disease resistances in tomato against Tomato yellow leaf curl
virus, late blight, and verticillium wilt. Euphytica, 205(2), pp.599-613.
Lazebnik, J., Tibboel, M., Dicke, M. and Loon, J.J., 2017. Inoculation of susceptible and
resistant potato plants with the late blight pathogen Phytophthora infestans: effects on an
aphid and its parasitoid. Entomologia Experimentalis et Applicata, 163(3), pp.305-314.
Luan, Y., Cui, J., Li, J., Jiang, N., Liu, P. and Meng, J., 2018. Effective enhancement of
resistance to Phytophthora infestans by overexpression of miR172a and b in Solanum
lycopersicum. Planta, 247(1), pp.127-138.
Ohara, T., Ishida, Y., Kudou, R., Kakibuchi, K., Akimitsu, K., Izumori, K. and Tajima, S.,
Kagawa University and Mitsui Agro Chemicals Inc, 2015. Plant disease control agent
comprising D-tagatose as active ingredient, and plant disease control method. U.S. Patent
9,125,409.
Seidl Johnson, A.C., Jordan, S.A. and Gevens, A.J., 2014. Novel resistance in heirloom
tomatoes and effectiveness of resistance in hybrids to Phytophthora infestans US-22, US-23,
and US-24 clonal lineages. Plant Disease, 98(6), pp.761-765.
Straquadine, G.S., Baig, M.B. and Mukhtar, M., 2017. Journal of Experimental Biology and
Agricultural Sciences. Journal of Experimental Biology.

6GENOMIC DISEASE RESISTANCE AGAINST LATE BLIGHT OF TOMATO
Zuluaga, A.P., Vega‐Arreguín, J.C., Fei, Z., Matas, A.J., Patev, S., Fry, W.E. and Rose, J.K.,
2016. Analysis of the tomato leaf transcriptome during successive hemibiotrophic stages of a
compatible interaction with the oomycete pathogen Phytophthora infestans. Molecular plant
pathology, 17(1), pp.42-54.